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41 results

common.inc

Blame
  • Nathaniel Catchpole's avatar
    Issue #2067017 by damiankloip: Remove usage of DRUPAL_CORE_COMPATIBILITY/VERSION constants.
    catch authored
    085a24e0
    History
    Code owners
    Assign users and groups as approvers for specific file changes. Learn more.
    common.inc 180.96 KiB
    <?php
    
    use Drupal\Component\Utility\Crypt;
    use Drupal\Component\Utility\Json;
    use Drupal\Component\Utility\SortArray;
    use Drupal\Component\Utility\String;
    use Drupal\Component\Utility\Tags;
    use Drupal\Component\Utility\Url;
    use Drupal\Component\Utility\Xss;
    use Drupal\Core\Cache\Cache;
    use Drupal\Core\Language\Language;
    use Symfony\Component\Yaml\Parser;
    use Symfony\Component\HttpFoundation\Response;
    use Symfony\Component\HttpFoundation\Request;
    use Drupal\Component\PhpStorage\PhpStorageFactory;
    use Drupal\Component\Utility\MapArray;
    use Drupal\Component\Utility\NestedArray;
    use Drupal\Core\Cache\CacheBackendInterface;
    use Drupal\Core\Datetime\DrupalDateTime;
    use Drupal\Core\Routing\GeneratorNotInitializedException;
    use Drupal\Core\SystemListingInfo;
    use Drupal\Core\Template\Attribute;
    
    /**
     * @file
     * Common functions that many Drupal modules will need to reference.
     *
     * The functions that are critical and need to be available even when serving
     * a cached page are instead located in bootstrap.inc.
     */
    
    /**
     * @defgroup php_wrappers PHP wrapper functions
     * @{
     * Functions that are wrappers or custom implementations of PHP functions.
     *
     * Certain PHP functions should not be used in Drupal. Instead, Drupal's
     * replacement functions should be used.
     *
     * For example, for improved or more secure UTF8-handling, or RFC-compliant
     * handling of URLs in Drupal.
     *
     * For ease of use and memorizing, all these wrapper functions use the same name
     * as the original PHP function, but prefixed with "drupal_". Beware, however,
     * that not all wrapper functions support the same arguments as the original
     * functions.
     *
     * You should always use these wrapper functions in your code.
     *
     * Wrong:
     * @code
     *   $my_substring = substr($original_string, 0, 5);
     * @endcode
     *
     * Correct:
     * @code
     *   $my_substring = drupal_substr($original_string, 0, 5);
     * @endcode
     *
     * @}
     */
    
    /**
     * Return status for saving which involved creating a new item.
     */
    const SAVED_NEW = 1;
    
    /**
     * Return status for saving which involved an update to an existing item.
     */
    const SAVED_UPDATED = 2;
    
    /**
     * Return status for saving which deleted an existing item.
     */
    const SAVED_DELETED = 3;
    
    /**
     * The default aggregation group for CSS files added to the page.
     */
    const CSS_AGGREGATE_DEFAULT = 0;
    
    /**
     * The default aggregation group for theme CSS files added to the page.
     */
    const CSS_AGGREGATE_THEME = 100;
    
    /**
     * The default weight for CSS rules that style HTML elements ("base" styles).
     */
    const CSS_BASE = -200;
    
    /**
     * The default weight for CSS rules that layout a page.
     */
    const CSS_LAYOUT = -100;
    
    /**
     * The default weight for CSS rules that style design components (and their associated states and skins.)
     */
    const CSS_COMPONENT = 0;
    
    /**
     * The default weight for CSS rules that style states and are not included with components.
     */
    const CSS_STATE = 100;
    
    /**
     * The default weight for CSS rules that style skins and are not included with components.
     */
    const CSS_SKIN = 200;
    
    /**
     * The default group for JavaScript settings added to the page.
     */
    const JS_SETTING = -200;
    
    /**
     * The default group for JavaScript and jQuery libraries added to the page.
     */
    const JS_LIBRARY = -100;
    
    /**
     * The default group for module JavaScript code added to the page.
     */
    const JS_DEFAULT = 0;
    
    /**
     * The default group for theme JavaScript code added to the page.
     */
    const JS_THEME = 100;
    
    /**
     * @defgroup block_caching Block Caching
     * @{
     * Constants that define each block's caching state.
     *
     * Modules specify how their blocks can be cached in their hook_block_info()
     * implementations. Caching can be turned off (DRUPAL_NO_CACHE), managed by the
     * module declaring the block (DRUPAL_CACHE_CUSTOM), or managed by the core
     * Block module. If the Block module is managing the cache, you can specify that
     * the block is the same for every page and user (DRUPAL_CACHE_GLOBAL), or that
     * it can change depending on the page (DRUPAL_CACHE_PER_PAGE) or by user
     * (DRUPAL_CACHE_PER_ROLE or DRUPAL_CACHE_PER_USER). Page and user settings can
     * be combined with a bitwise-binary or operator; for example,
     * DRUPAL_CACHE_PER_ROLE | DRUPAL_CACHE_PER_PAGE means that the block can change
     * depending on the user role or page it is on.
     *
     * The block cache is cleared when the 'content' cache tag is invalidated,
     * following the same pattern as the page cache (node, comment, user, taxonomy
     * added or updated...).
     *
     * Note that user 1 is excluded from block caching.
     */
    
    /**
     * The block should not get cached.
     *
     * This setting should be used:
     * - For simple blocks (notably those that do not perform any db query), where
     *   querying the db cache would be more expensive than directly generating the
     *   content.
     * - For blocks that change too frequently.
     */
    const DRUPAL_NO_CACHE = -1;
    
    /**
     * The block is handling its own caching in its hook_block_view().
     *
     * This setting is useful when time based expiration is needed or a site uses a
     * node access which invalidates standard block cache.
     */
    const DRUPAL_CACHE_CUSTOM = -2;
    
    /**
     * The block or element can change depending on the user's roles.
     *
     * This is the default setting for blocks, used when the block does not specify
     * anything.
     */
    const DRUPAL_CACHE_PER_ROLE = 0x0001;
    
    /**
     * The block or element can change depending on the user.
     *
     * This setting can be resource-consuming for sites with large number of users,
     * and thus should only be used when DRUPAL_CACHE_PER_ROLE is not sufficient.
     */
    const DRUPAL_CACHE_PER_USER = 0x0002;
    
    /**
     * The block or element can change depending on the page being viewed.
     */
    const DRUPAL_CACHE_PER_PAGE = 0x0004;
    
    /**
     * The block or element is the same for every user and page that it is visible.
     */
    const DRUPAL_CACHE_GLOBAL = 0x0008;
    
    /**
     * @} End of "defgroup block_caching".
     */
    
    /**
     * The delimiter used to split plural strings.
     *
     * This is the ETX (End of text) character and is used as a minimal means to
     * separate singular and plural variants in source and translation text. It
     * was found to be the most compatible delimiter for the supported databases.
     */
    const LOCALE_PLURAL_DELIMITER = "\03";
    
    /**
     * Adds content to a specified region.
     *
     * @param $region
     *   Page region the content is added to.
     * @param $data
     *   Content to be added.
     */
    function drupal_add_region_content($region = NULL, $data = NULL) {
      static $content = array();
    
      if (isset($region) && isset($data)) {
        $content[$region][] = $data;
      }
      return $content;
    }
    
    /**
     * Gets assigned content for a given region.
     *
     * @param $region
     *   A specified region to fetch content for. If NULL, all regions will be
     *   returned.
     * @param $delimiter
     *   Content to be inserted between imploded array elements.
     */
    function drupal_get_region_content($region = NULL, $delimiter = ' ') {
      $content = drupal_add_region_content();
      if (isset($region)) {
        if (isset($content[$region]) && is_array($content[$region])) {
          return implode($delimiter, $content[$region]);
        }
      }
      else {
        foreach (array_keys($content) as $region) {
          if (is_array($content[$region])) {
            $content[$region] = implode($delimiter, $content[$region]);
          }
        }
        return $content;
      }
    }
    
    /**
     * Gets the name of the currently active installation profile.
     *
     * When this function is called during Drupal's initial installation process,
     * the name of the profile that's about to be installed is stored in the global
     * installation state. At all other times, the standard Drupal systems variable
     * table contains the name of the current profile, and we can call
     * variable_get() to determine what one is active.
     *
     * @return $profile
     *   The name of the installation profile.
     */
    function drupal_get_profile() {
      global $install_state;
    
      if (isset($install_state['parameters']['profile'])) {
        $profile = $install_state['parameters']['profile'];
      }
      else {
        $profile = variable_get('install_profile', 'standard');
      }
    
      return $profile;
    }
    
    
    /**
     * Sets the breadcrumb trail for the current page.
     *
     * @param $breadcrumb
     *   Array of links, starting with "home" and proceeding up to but not including
     *   the current page.
     *
     * @deprecated This will be removed in 8.0. Instead, register a new breadcrumb
     *   builder service.
     *
     * @see Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface
     */
    function drupal_set_breadcrumb($breadcrumb = NULL) {
      $stored_breadcrumb = &drupal_static(__FUNCTION__);
    
      if (isset($breadcrumb)) {
        $stored_breadcrumb = $breadcrumb;
      }
      return $stored_breadcrumb;
    }
    
    /**
     * Adds output to the HEAD tag of the HTML page.
     *
     * This function can be called as long as the headers aren't sent. Pass no
     * arguments (or NULL for both) to retrieve the currently stored elements.
     *
     * @param $data
     *   A renderable array. If the '#type' key is not set then 'html_tag' will be
     *   added as the default '#type'.
     * @param $key
     *   A unique string key to allow implementations of hook_html_head_alter() to
     *   identify the element in $data. Required if $data is not NULL.
     *
     * @return
     *   An array of all stored HEAD elements.
     *
     * @see drupal_pre_render_html_tag()
     */
    function drupal_add_html_head($data = NULL, $key = NULL) {
      $stored_head = &drupal_static(__FUNCTION__);
    
      if (!isset($stored_head)) {
        // Make sure the defaults, including Content-Type, come first.
        $stored_head = _drupal_default_html_head();
      }
    
      if (isset($data) && isset($key)) {
        if (!isset($data['#type'])) {
          $data['#type'] = 'html_tag';
        }
        $stored_head[$key] = $data;
      }
      return $stored_head;
    }
    
    /**
     * Returns elements that are always displayed in the HEAD tag of the HTML page.
     */
    function _drupal_default_html_head() {
      // Add default elements. Make sure the Content-Type comes first because the
      // IE browser may be vulnerable to XSS via encoding attacks from any content
      // that comes before this META tag, such as a TITLE tag.
      $elements['system_meta_content_type'] = array(
        '#type' => 'html_tag',
        '#tag' => 'meta',
        '#attributes' => array(
          'charset' => 'utf-8',
        ),
        // Security: This always has to be output first.
        '#weight' => -1000,
      );
      // Show Drupal and the major version number in the META GENERATOR tag.
      // Get the major version.
      list($version, ) = explode('.', Drupal::VERSION);
      $elements['system_meta_generator'] = array(
        '#type' => 'html_tag',
        '#tag' => 'meta',
        '#attributes' => array(
          'name' => 'Generator',
          'content' => 'Drupal ' . $version . ' (http://drupal.org)',
        ),
      );
      // Also send the generator in the HTTP header.
      $elements['system_meta_generator']['#attached']['drupal_add_http_header'][] = array('X-Generator', $elements['system_meta_generator']['#attributes']['content']);
      return $elements;
    }
    
    /**
     * Retrieves output to be displayed in the HEAD tag of the HTML page.
     */
    function drupal_get_html_head() {
      $elements = drupal_add_html_head();
      drupal_alter('html_head', $elements);
      return drupal_render($elements);
    }
    
    /**
     * Adds a feed URL for the current page.
     *
     * This function can be called as long the HTML header hasn't been sent.
     *
     * @param $url
     *   An internal system path or a fully qualified external URL of the feed.
     * @param $title
     *   The title of the feed.
     */
    function drupal_add_feed($url = NULL, $title = '') {
      $stored_feed_links = &drupal_static(__FUNCTION__, array());
    
      if (isset($url)) {
        $stored_feed_links[$url] = theme('feed_icon', array('url' => $url, 'title' => $title));
    
        drupal_add_html_head_link(array(
          'rel' => 'alternate',
          'type' => 'application/rss+xml',
          'title' => $title,
          // Force the URL to be absolute, for consistency with other <link> tags
          // output by Drupal.
          'href' => url($url, array('absolute' => TRUE)),
        ));
      }
      return $stored_feed_links;
    }
    
    /**
     * Gets the feed URLs for the current page.
     *
     * @param $delimiter
     *   A delimiter to split feeds by.
     */
    function drupal_get_feeds($delimiter = "\n") {
      $feeds = drupal_add_feed();
      return implode($feeds, $delimiter);
    }
    
    /**
     * @defgroup http_handling HTTP handling
     * @{
     * Functions to properly handle HTTP responses.
     */
    
    /**
     * Processes a URL query parameter array to remove unwanted elements.
     *
     * @param $query
     *   (optional) An array to be processed. Defaults to $_GET.
     * @param $exclude
     *   (optional) A list of $query array keys to remove. Use "parent[child]" to
     *   exclude nested items.
     * @param $parent
     *   Internal use only. Used to build the $query array key for nested items.
     *
     * @return
     *   An array containing query parameters, which can be used for url().
     *
     * @deprecated as of Drupal 8.0. Use Url::filterQueryParameters() instead.
     */
    function drupal_get_query_parameters(array $query = NULL, array $exclude = array(), $parent = '') {
      if (!isset($query)) {
        $query = Drupal::request()->query->all();
      }
      return Url::filterQueryParameters($query, $exclude, $parent);
    }
    
    /**
     * Parses an array into a valid, rawurlencoded query string.
     *
     * @see drupal_get_query_parameters()
     * @deprecated as of Drupal 8.0. Use Url::buildQuery() instead.
     * @ingroup php_wrappers
     *
     * @deprecated as of Drupal 8.0. Use Url::buildQuery() instead.
     */
    function drupal_http_build_query(array $query, $parent = '') {
      return Url::buildQuery($query, $parent);
    }
    
    /**
     * Prepares a 'destination' URL query parameter for use with url().
     *
     * Used to direct the user back to the referring page after completing a form.
     * By default the current URL is returned. If a destination exists in the
     * previous request, that destination is returned. As such, a destination can
     * persist across multiple pages.
     *
     * @return
     *   An associative array containing the key:
     *   - destination: The path provided via the destination query string or, if
     *     not available, the current path.
     *
     * @see current_path()
     */
    function drupal_get_destination() {
      $destination = &drupal_static(__FUNCTION__);
    
      if (isset($destination)) {
        return $destination;
      }
    
      $query = Drupal::request()->query;
      if ($query->has('destination')) {
        $destination = array('destination' => $query->get('destination'));
      }
      else {
        $path = current_path();
        $query = Url::buildQuery(Url::filterQueryParameters($query->all()));
        if ($query != '') {
          $path .= '?' . $query;
        }
        $destination = array('destination' => $path);
      }
      return $destination;
    }
    
    /**
     * Parses a system URL string into an associative array suitable for url().
     *
     * This function should only be used for URLs that have been generated by the
     * system, such as via url(). It should not be used for URLs that come from
     * external sources, or URLs that link to external resources.
     *
     * The returned array contains a 'path' that may be passed separately to url().
     * For example:
     * @code
     *   $options = drupal_parse_url($_GET['destination']);
     *   $my_url = url($options['path'], $options);
     *   $my_link = l('Example link', $options['path'], $options);
     * @endcode
     *
     * This is required, because url() does not support relative URLs containing a
     * query string or fragment in its $path argument. Instead, any query string
     * needs to be parsed into an associative query parameter array in
     * $options['query'] and the fragment into $options['fragment'].
     *
     * @param $url
     *   The URL string to parse, f.e. $_GET['destination'].
     *
     * @return
     *   An associative array containing the keys:
     *   - 'path': The path of the URL. If the given $url is external, this includes
     *     the scheme and host.
     *   - 'query': An array of query parameters of $url, if existent.
     *   - 'fragment': The fragment of $url, if existent.
     *
     * @see url()
     * @ingroup php_wrappers
     *
     * @deprecated as of Drupal 8.0. Use Url::parse() instead.
     */
    function drupal_parse_url($url) {
      return Url::parse($url);
    }
    
    /**
     * Encodes a Drupal path for use in a URL.
     *
     * For aesthetic reasons slashes are not escaped.
     *
     * Note that url() takes care of calling this function, so a path passed to that
     * function should not be encoded in advance.
     *
     * @param $path
     *   The Drupal path to encode.
     *
     * @deprecated as of Drupal 8.0. Use Url::encodePath() instead.
     */
    function drupal_encode_path($path) {
      return Url::encodePath($path);
    }
    
    /**
     * Determines if an external URL points to this Drupal installation.
     *
     * @param $url
     *   A string containing an external URL, such as "http://example.com/foo".
     *
     * @return
     *   TRUE if the URL has the same domain and base path.
     *
     * @deprecated as of Drupal 8.0. Use Url::externalIsLocal() instead.
     */
    function _external_url_is_local($url) {
      return Url::externalIsLocal($url, base_path());
    }
    
    /**
     * Helper function for determining hosts excluded from needing a proxy.
     *
     * @return
     *   TRUE if a proxy should be used for this host.
     */
    function _drupal_http_use_proxy($host) {
      $proxy_exceptions = settings()->get('proxy_exceptions', array('localhost', '127.0.0.1'));
      return !in_array(strtolower($host), $proxy_exceptions, TRUE);
    }
    
    /**
     * @} End of "defgroup http_handling".
     */
    
    /**
     * @defgroup validation Input validation
     * @{
     * Functions to validate user input.
     */
    
    /**
     * Verifies the syntax of the given e-mail address.
     *
     * This uses the
     * @link http://php.net/manual/filter.filters.validate.php PHP e-mail validation filter. @endlink
     *
     * @param $mail
     *   A string containing an e-mail address.
     *
     * @return
     *   TRUE if the address is in a valid format.
     */
    function valid_email_address($mail) {
      return (bool)filter_var($mail, FILTER_VALIDATE_EMAIL);
    }
    
    /**
     * Verifies the syntax of the given URL.
     *
     * This function should only be used on actual URLs. It should not be used for
     * Drupal menu paths, which can contain arbitrary characters.
     * Valid values per RFC 3986.
     * @param $url
     *   The URL to verify.
     * @param $absolute
     *   Whether the URL is absolute (beginning with a scheme such as "http:").
     *
     * @return
     *   TRUE if the URL is in a valid format.
     *
     * @see \Drupal\Component\Utility\Url::isValid()
     *
     * @deprecated as of Drupal 8.0. Use Url::isValid() instead.
     */
    function valid_url($url, $absolute = FALSE) {
      return Url::isValid($url, $absolute);
    }
    
    /**
     * Verifies that a number is a multiple of a given step.
     *
     * The implementation assumes it is dealing with IEEE 754 double precision
     * floating point numbers that are used by PHP on most systems.
     *
     * This is based on the number/range verification methods of webkit.
     *
     * @param $value
     *   The value that needs to be checked.
     * @param $step
     *   The step scale factor. Must be positive.
     * @param $offset
     *   (optional) An offset, to which the difference must be a multiple of the
     *   given step.
     *
     * @return bool
     *   TRUE if no step mismatch has occured, or FALSE otherwise.
     *
     * @see http://opensource.apple.com/source/WebCore/WebCore-1298/html/NumberInputType.cpp
     */
    function valid_number_step($value, $step, $offset = 0.0) {
      $double_value = (double) abs($value - $offset);
    
      // The fractional part of a double has 53 bits. The greatest number that could
      // be represented with that is 2^53. If the given value is even bigger than
      // $step * 2^53, then dividing by $step will result in a very small remainder.
      // Since that remainder can't even be represented with a single precision
      // float the following computation of the remainder makes no sense and we can
      // safely ignore it instead.
      if ($double_value / pow(2.0, 53) > $step) {
        return TRUE;
      }
    
      // Now compute that remainder of a division by $step.
      $remainder = (double) abs($double_value - $step * round($double_value / $step));
    
      // $remainder is a double precision floating point number. Remainders that
      // can't be represented with single precision floats are acceptable. The
      // fractional part of a float has 24 bits. That means remainders smaller than
      // $step * 2^-24 are acceptable.
      $computed_acceptable_error = (double)($step / pow(2.0, 24));
    
      return $computed_acceptable_error >= $remainder || $remainder >= ($step - $computed_acceptable_error);
    }
    
    /**
     * @} End of "defgroup validation".
     */
    
    /**
     * @defgroup sanitization Sanitization functions
     * @{
     * Functions to sanitize values.
     *
     * See http://drupal.org/writing-secure-code for information
     * on writing secure code.
     */
    
    /**
     * Strips dangerous protocols (e.g. 'javascript:') from a URI.
     *
     * This function must be called for all URIs within user-entered input prior
     * to being output to an HTML attribute value. It is often called as part of
     * check_url() or filter_xss(), but those functions return an HTML-encoded
     * string, so this function can be called independently when the output needs to
     * be a plain-text string for passing to t(), l(),
     * Drupal\Core\Template\Attribute, or another function that will call
     * check_plain() separately.
     *
     * @param $uri
     *   A plain-text URI that might contain dangerous protocols.
     *
     * @return
     *   A plain-text URI stripped of dangerous protocols. As with all plain-text
     *   strings, this return value must not be output to an HTML page without
     *   check_plain() being called on it. However, it can be passed to functions
     *   expecting plain-text strings.
     *
     * @see \Drupal\Component\Utility\Url::stripDangerousProtocols()
     */
    function drupal_strip_dangerous_protocols($uri) {
      return Url::stripDangerousProtocols($uri);
    }
    
    /**
     * Strips dangerous protocols from a URI and encodes it for output to HTML.
     *
     * @param $uri
     *   A plain-text URI that might contain dangerous protocols.
     *
     * @return
     *   A URI stripped of dangerous protocols and encoded for output to an HTML
     *   attribute value. Because it is already encoded, it should not be set as a
     *   value within a $attributes array passed to Drupal\Core\Template\Attribute,
     *   because Drupal\Core\Template\Attribute expects those values to be
     *   plain-text strings. To pass a filtered URI to
     *   Drupal\Core\Template\Attribute, call drupal_strip_dangerous_protocols()
     *   instead.
     *
     * @see \Drupal\Component\Utility\Url::stripDangerousProtocols()
     * @see \Drupal\Component\Utility\String::checkPlain()
     */
    function check_url($uri) {
      return String::checkPlain(Url::stripDangerousProtocols($uri));
    }
    
    /**
     * Applies a very permissive XSS/HTML filter for admin-only use.
     *
     * Use only for fields where it is impractical to use the
     * whole filter system, but where some (mainly inline) mark-up
     * is desired (so check_plain() is not acceptable).
     *
     * Allows all tags that can be used inside an HTML body, save
     * for scripts and styles.
     *
     * @param string $string
     *   The string to apply the filter to.
     *
     * @return string
     *   The filtered string.
     *
     * @see \Drupal\Component\Utility\Xss::filterAdmin()
     */
    function filter_xss_admin($string) {
      return Xss::filterAdmin($string);
    }
    
    /**
     * Filters HTML to prevent cross-site-scripting (XSS) vulnerabilities.
     *
     * Based on kses by Ulf Harnhammar, see http://sourceforge.net/projects/kses.
     * For examples of various XSS attacks, see: http://ha.ckers.org/xss.html.
     *
     * This code does four things:
     * - Removes characters and constructs that can trick browsers.
     * - Makes sure all HTML entities are well-formed.
     * - Makes sure all HTML tags and attributes are well-formed.
     * - Makes sure no HTML tags contain URLs with a disallowed protocol (e.g.
     *   javascript:).
     *
     * @param $string
     *   The string with raw HTML in it. It will be stripped of everything that can
     *   cause an XSS attack.
     * @param $allowed_tags
     *   An array of allowed tags.
     *
     * @return
     *   An XSS safe version of $string, or an empty string if $string is not
     *   valid UTF-8.
     *
     * @see \Drupal\Component\Utility\Xss::filter()
     *
     * @ingroup sanitization
     */
    function filter_xss($string, $allowed_tags = array('a', 'em', 'strong', 'cite', 'blockquote', 'code', 'ul', 'ol', 'li', 'dl', 'dt', 'dd')) {
      return Xss::filter($string, $allowed_tags);
    }
    
    /**
     * Processes an HTML attribute value and strips dangerous protocols from URLs.
     *
     * @param string $string
     *   The string with the attribute value.
     *
     * @return string
     *   Cleaned up and HTML-escaped version of $string.
     *
     * @see \Drupal\Component\Utility\Url::filterBadProtocol()
     */
    function filter_xss_bad_protocol($string) {
      return Url::filterBadProtocol($string);
    }
    
    /**
     * @} End of "defgroup sanitization".
     */
    
    /**
     * @defgroup format Formatting
     * @{
     * Functions to format numbers, strings, dates, etc.
     */
    
    /**
     * Formats an RSS channel.
     *
     * Arbitrary elements may be added using the $args associative array.
     */
    function format_rss_channel($title, $link, $description, $items, $langcode = NULL, $args = array()) {
      $langcode = $langcode ? $langcode : language(Language::TYPE_CONTENT)->id;
    
      $output = "<channel>\n";
      $output .= ' <title>' . check_plain($title) . "</title>\n";
      $output .= ' <link>' . check_url($link) . "</link>\n";
    
      // The RSS 2.0 "spec" doesn't indicate HTML can be used in the description.
      // We strip all HTML tags, but need to prevent double encoding from properly
      // escaped source data (such as &amp becoming &amp;amp;).
      $output .= ' <description>' . check_plain(decode_entities(strip_tags($description))) . "</description>\n";
      $output .= ' <language>' . check_plain($langcode) . "</language>\n";
      $output .= format_xml_elements($args);
      $output .= $items;
      $output .= "</channel>\n";
    
      return $output;
    }
    
    /**
     * Formats a single RSS item.
     *
     * Arbitrary elements may be added using the $args associative array.
     */
    function format_rss_item($title, $link, $description, $args = array()) {
      $output = "<item>\n";
      $output .= ' <title>' . check_plain($title) . "</title>\n";
      $output .= ' <link>' . check_url($link) . "</link>\n";
      $output .= ' <description>' . check_plain($description) . "</description>\n";
      $output .= format_xml_elements($args);
      $output .= "</item>\n";
    
      return $output;
    }
    
    /**
     * Formats XML elements.
     *
     * @param $array
     *   An array where each item represents an element and is either a:
     *   - (key => value) pair (<key>value</key>)
     *   - Associative array with fields:
     *     - 'key': element name
     *     - 'value': element contents
     *     - 'attributes': associative array of element attributes
     *
     * In both cases, 'value' can be a simple string, or it can be another array
     * with the same format as $array itself for nesting.
     */
    function format_xml_elements($array) {
      $output = '';
      foreach ($array as $key => $value) {
        if (is_numeric($key)) {
          if ($value['key']) {
            $output .= ' <' . $value['key'];
            if (isset($value['attributes']) && is_array($value['attributes'])) {
              $output .= new Attribute($value['attributes']);
            }
    
            if (isset($value['value']) && $value['value'] != '') {
              $output .= '>' . (is_array($value['value']) ? format_xml_elements($value['value']) : check_plain($value['value'])) . '</' . $value['key'] . ">\n";
            }
            else {
              $output .= " />\n";
            }
          }
        }
        else {
          $output .= ' <' . $key . '>' . (is_array($value) ? format_xml_elements($value) : check_plain($value)) . "</$key>\n";
        }
      }
      return $output;
    }
    
    /**
     * Formats a string containing a count of items.
     *
     * This function ensures that the string is pluralized correctly. Since t() is
     * called by this function, make sure not to pass already-localized strings to
     * it.
     *
     * For example:
     * @code
     *   $output = format_plural($node->comment_count, '1 comment', '@count comments');
     * @endcode
     *
     * Example with additional replacements:
     * @code
     *   $output = format_plural($update_count,
     *     'Changed the content type of 1 post from %old-type to %new-type.',
     *     'Changed the content type of @count posts from %old-type to %new-type.',
     *     array('%old-type' => $info->old_type, '%new-type' => $info->new_type));
     * @endcode
     *
     * @param $count
     *   The item count to display.
     * @param $singular
     *   The string for the singular case. Make sure it is clear this is singular,
     *   to ease translation (e.g. use "1 new comment" instead of "1 new"). Do not
     *   use @count in the singular string.
     * @param $plural
     *   The string for the plural case. Make sure it is clear this is plural, to
     *   ease translation. Use @count in place of the item count, as in
     *   "@count new comments".
     * @param $args
     *   An associative array of replacements to make after translation. Instances
     *   of any key in this array are replaced with the corresponding value.
     *   Based on the first character of the key, the value is escaped and/or
     *   themed. See format_string(). Note that you do not need to include @count
     *   in this array; this replacement is done automatically for the plural case.
     * @param $options
     *   An associative array of additional options. See t() for allowed keys.
     *
     * @return
     *   A translated string.
     *
     * @see t()
     * @see format_string()
     */
    function format_plural($count, $singular, $plural, array $args = array(), array $options = array()) {
      $args['@count'] = $count;
      // Join both forms to search a translation.
      $tranlatable_string = implode(LOCALE_PLURAL_DELIMITER, array($singular, $plural));
      // Translate as usual.
      $translated_strings = t($tranlatable_string, $args, $options);
      // Split joined translation strings into array.
      $translated_array = explode(LOCALE_PLURAL_DELIMITER, $translated_strings);
    
      if ($count == 1) {
        return $translated_array[0];
      }
    
      // Get the plural index through the gettext formula.
      // @todo implement static variable to minimize function_exists() usage.
      $index = (function_exists('locale_get_plural')) ? locale_get_plural($count, isset($options['langcode']) ? $options['langcode'] : NULL) : -1;
      if ($index == 0) {
        // Singular form.
        return $translated_array[0];
      }
      else {
        if (isset($translated_array[$index])) {
          // N-th plural form.
          return $translated_array[$index];
        }
        else {
          // If the index cannot be computed or there's no translation, use
          // the second plural form as a fallback (which allows for most flexiblity
          // with the replaceable @count value).
          return $translated_array[1];
        }
      }
    }
    
    /**
     * Parses a given byte count.
     *
     * @param $size
     *   A size expressed as a number of bytes with optional SI or IEC binary unit
     *   prefix (e.g. 2, 3K, 5MB, 10G, 6GiB, 8 bytes, 9mbytes).
     *
     * @return
     *   An integer representation of the size in bytes.
     */
    function parse_size($size) {
      $unit = preg_replace('/[^bkmgtpezy]/i', '', $size); // Remove the non-unit characters from the size.
      $size = preg_replace('/[^0-9\.]/', '', $size); // Remove the non-numeric characters from the size.
      if ($unit) {
        // Find the position of the unit in the ordered string which is the power of magnitude to multiply a kilobyte by.
        return round($size * pow(DRUPAL_KILOBYTE, stripos('bkmgtpezy', $unit[0])));
      }
      else {
        return round($size);
      }
    }
    
    /**
     * Generates a string representation for the given byte count.
     *
     * @param $size
     *   A size in bytes.
     * @param $langcode
     *   Optional language code to translate to a language other than what is used
     *   to display the page.
     *
     * @return
     *   A translated string representation of the size.
     */
    function format_size($size, $langcode = NULL) {
      if ($size < DRUPAL_KILOBYTE) {
        return format_plural($size, '1 byte', '@count bytes', array(), array('langcode' => $langcode));
      }
      else {
        $size = $size / DRUPAL_KILOBYTE; // Convert bytes to kilobytes.
        $units = array(
          t('@size KB', array(), array('langcode' => $langcode)),
          t('@size MB', array(), array('langcode' => $langcode)),
          t('@size GB', array(), array('langcode' => $langcode)),
          t('@size TB', array(), array('langcode' => $langcode)),
          t('@size PB', array(), array('langcode' => $langcode)),
          t('@size EB', array(), array('langcode' => $langcode)),
          t('@size ZB', array(), array('langcode' => $langcode)),
          t('@size YB', array(), array('langcode' => $langcode)),
        );
        foreach ($units as $unit) {
          if (round($size, 2) >= DRUPAL_KILOBYTE) {
            $size = $size / DRUPAL_KILOBYTE;
          }
          else {
            break;
          }
        }
        return str_replace('@size', round($size, 2), $unit);
      }
    }
    
    /**
     * Formats a time interval with the requested granularity.
     *
     * @param $interval
     *   The length of the interval in seconds.
     * @param $granularity
     *   How many different units to display in the string.
     * @param $langcode
     *   Optional language code to translate to a language other than
     *   what is used to display the page.
     *
     * @return
     *   A translated string representation of the interval.
     */
    function format_interval($interval, $granularity = 2, $langcode = NULL) {
      $units = array(
        '1 year|@count years' => 31536000,
        '1 month|@count months' => 2592000,
        '1 week|@count weeks' => 604800,
        '1 day|@count days' => 86400,
        '1 hour|@count hours' => 3600,
        '1 min|@count min' => 60,
        '1 sec|@count sec' => 1
      );
      $output = '';
      foreach ($units as $key => $value) {
        $key = explode('|', $key);
        if ($interval >= $value) {
          $output .= ($output ? ' ' : '') . format_plural(floor($interval / $value), $key[0], $key[1], array(), array('langcode' => $langcode));
          $interval %= $value;
          $granularity--;
        }
    
        if ($granularity == 0) {
          break;
        }
      }
      return $output ? $output : t('0 sec', array(), array('langcode' => $langcode));
    }
    
    /**
     * Formats a date, using a date type or a custom date format string.
     *
     * @param $timestamp
     *   A UNIX timestamp to format.
     * @param $type
     *   (optional) The format to use, one of:
     *   - One of the built-in formats: 'short', 'medium',
     *     'long', 'html_datetime', 'html_date', 'html_time',
     *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
     *   - The name of a date type defined by a module in
     *     hook_date_format_types(), if it's been assigned a format.
     *   - The machine name of an administrator-defined date format.
     *   - 'custom', to use $format.
     *   Defaults to 'medium'.
     * @param $format
     *   (optional) If $type is 'custom', a PHP date format string suitable for
     *   input to date(). Use a backslash to escape ordinary text, so it does not
     *   get interpreted as date format characters.
     * @param $timezone
     *   (optional) Time zone identifier, as described at
     *   http://php.net/manual/timezones.php Defaults to the time zone used to
     *   display the page.
     * @param $langcode
     *   (optional) Language code to translate to. Defaults to the language used to
     *   display the page.
     *
     * @return
     *   A translated date string in the requested format.
     *
     * @see \Drupal\Component\Datetime\Date::format()
     */
    function format_date($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL) {
      return Drupal::service('date')->format($timestamp, $type, $format, $timezone, $langcode);
    }
    
    /**
     * Returns an ISO8601 formatted date based on the given date.
     *
     * @param $date
     *   A UNIX timestamp.
     *
     * @return string
     *   An ISO8601 formatted date.
     */
    function date_iso8601($date) {
      // The DATE_ISO8601 constant cannot be used here because it does not match
      // date('c') and produces invalid RDF markup.
      return date('c', $date);
    }
    
    /**
     * Translates a formatted date string.
     *
     * Callback for preg_replace_callback() within format_date().
     */
    function _format_date_callback(array $matches = NULL, $new_langcode = NULL) {
      // We cache translations to avoid redundant and rather costly calls to t().
      static $cache, $langcode;
    
      if (!isset($matches)) {
        $langcode = $new_langcode;
        return;
      }
    
      $code = $matches[1];
      $string = $matches[2];
    
      if (!isset($cache[$langcode][$code][$string])) {
        $options = array(
          'langcode' => $langcode,
        );
    
        if ($code == 'F') {
          $options['context'] = 'Long month name';
        }
    
        if ($code == '') {
          $cache[$langcode][$code][$string] = $string;
        }
        else {
          $cache[$langcode][$code][$string] = t($string, array(), $options);
        }
      }
      return $cache[$langcode][$code][$string];
    }
    
    /**
     * Retrieves the correct datetime format type for this system.
     *
     * This value is sometimes required when the format type needs to be determined
     * before a date can be created.
     *
     * @return string
     *   A string as defined in \DrupalComponent\Datetime\DateTimePlus.php: either
     *   'intl' or 'php', depending on whether IntlDateFormatter is available.
     */
    function datetime_default_format_type() {
      static $drupal_static_fast;
      if (!isset($drupal_static_fast)) {
        $drupal_static_fast['format_type'] = &drupal_static(__FUNCTION__);
      }
      $format_type = &$drupal_static_fast['format_type'];
    
      if (!isset($format_type)) {
        $date = new DrupalDateTime();
        $format_type = $date->canUseIntl() ? DrupalDateTime::INTL : DrupalDateTime::PHP;
      }
      return $format_type;
    }
    
    /**
     * @} End of "defgroup format".
     */
    
    /**
     * Generates an internal or external URL.
     *
     * When creating links in modules, consider whether l() could be a better
     * alternative than url().
     *
     * @see \Drupal\Core\Routing\UrlGeneratorInterface::generateFromPath().
     */
    function url($path = NULL, array $options = array()) {
      $generator = Drupal::urlGenerator();
      try {
        $url = $generator->generateFromPath($path, $options);
      }
      catch (GeneratorNotInitializedException $e) {
        // Fallback to using globals.
        // @todo Remove this once there is no code that calls url() when there is
        //   no request.
        global $base_url, $base_path, $script_path;
        $generator->setBasePath($base_path);
        $generator->setBaseUrl($base_url . '/');
        $generator->setScriptPath($script_path);
        $url = $generator->generateFromPath($path, $options);
      }
      return $url;
    }
    
    /**
     * Returns TRUE if a path is external to Drupal (e.g. http://example.com).
     *
     * If a path cannot be assessed by Drupal's menu handler, then we must
     * treat it as potentially insecure.
     *
     * @param $path
     *   The internal path or external URL being linked to, such as "node/34" or
     *   "http://example.com/foo".
     *
     * @return
     *   Boolean TRUE or FALSE, where TRUE indicates an external path.
     */
    function url_is_external($path) {
      return Url::isExternal($path);
    }
    
    /**
     * Formats an attribute string for an HTTP header.
     *
     * @param $attributes
     *   An associative array of attributes such as 'rel'.
     *
     * @return
     *   A ; separated string ready for insertion in a HTTP header. No escaping is
     *   performed for HTML entities, so this string is not safe to be printed.
     *
     * @see drupal_add_http_header()
     */
    function drupal_http_header_attributes(array $attributes = array()) {
      foreach ($attributes as $attribute => &$data) {
        if (is_array($data)) {
          $data = implode(' ', $data);
        }
        $data = $attribute . '="' . $data . '"';
      }
      return $attributes ? ' ' . implode('; ', $attributes) : '';
    }
    
    /**
     * Formats an internal or external URL link as an HTML anchor tag.
     *
     * This function correctly handles aliased paths and adds an 'active' class
     * attribute to links that point to the current page (for theming), so all
     * internal links output by modules should be generated by this function if
     * possible.
     *
     * However, for links enclosed in translatable text you should use t() and
     * embed the HTML anchor tag directly in the translated string. For example:
     * @code
     * t('Visit the <a href="@url">settings</a> page', array('@url' => url('admin')));
     * @endcode
     * This keeps the context of the link title ('settings' in the example) for
     * translators.
     *
     * This function does not support generating links from internal routes. For
     * that use \Drupal\Core\Utility\LinkGenerator::generate(), which is exposed via
     * the 'link_generator' service. It requires an internal route name and does not
     * support external URLs. Using Drupal 7 style system paths should be avoided if
     * possible but l() should still be used when rendering links to external URLs.
     *
     * @param string|array $text
     *   The link text for the anchor tag as a translated string or render array.
     * @param string $path
     *   The internal path or external URL being linked to, such as "node/34" or
     *   "http://example.com/foo". After the url() function is called to construct
     *   the URL from $path and $options, the resulting URL is passed through
     *   check_plain() before it is inserted into the HTML anchor tag, to ensure
     *   well-formed HTML. See url() for more information and notes.
     * @param array $options
     *   An associative array of additional options. Defaults to an empty array. It
     *   may contain the following elements.
     *   - 'attributes': An associative array of HTML attributes to apply to the
     *     anchor tag. If element 'class' is included, it must be an array; 'title'
     *     must be a string; other elements are more flexible, as they just need
     *     to work as an argument for the constructor of the class
     *     Drupal\Core\Template\Attribute($options['attributes']).
     *   - 'html' (default FALSE): Whether $text is HTML or just plain-text. For
     *     example, to make an image tag into a link, this must be set to TRUE, or
     *     you will see the escaped HTML image tag. $text is not sanitized if
     *     'html' is TRUE. The calling function must ensure that $text is already
     *     safe.
     *   - 'language': An optional language object. If the path being linked to is
     *     internal to the site, $options['language'] is used to determine whether
     *     the link is "active", or pointing to the current page (the language as
     *     well as the path must match). This element is also used by url().
     *   - Additional $options elements used by the url() function.
     *
     * @return string
     *   An HTML string containing a link to the given path.
     *
     * @see url()
     */
    function l($text, $path, array $options = array()) {
      // Start building a structured representation of our link to be altered later.
      $variables = array(
        'text' => is_array($text) ? drupal_render($text) : $text,
        'path' => $path,
        'options' => $options,
      );
    
      // Merge in default options.
      $variables['options'] += array(
        'attributes' => array(),
        'query' => array(),
        'html' => FALSE,
        'language' => NULL,
      );
    
      // Add a hreflang attribute if we know the language of this link's url and
      // hreflang has not already been set.
      if (!empty($variables['options']['language']) && !isset($variables['options']['attributes']['hreflang'])) {
        $variables['options']['attributes']['hreflang'] = $variables['options']['language']->id;
      }
    
      // Because l() is called very often we statically cache values that require an
      // extra function call.
      static $drupal_static_fast;
      if (!isset($drupal_static_fast['active'])) {
        $drupal_static_fast['active'] = &drupal_static(__FUNCTION__);
      }
      $active = &$drupal_static_fast['active'];
      if (!isset($active)) {
        $active = array(
          'path' => current_path(),
          'front_page' => drupal_is_front_page(),
          'language' => language(Language::TYPE_URL)->id,
          'query' => Drupal::service('request')->query->all(),
        );
      }
    
      // Determine whether this link is "active', meaning that it links to the
      // current page. It is important that we stop checking "active" conditions if
      // we know the link is not active. This helps ensure that l() remains fast.
      // An active link's path is equal to the current path.
      $variables['url_is_active'] = ($path == $active['path'] || ($path == '<front>' && $active['front_page']))
      // The language of an active link is equal to the current language.
      && (empty($variables['options']['language']) || $variables['options']['language']->id == $active['language'])
      // The query parameters of an active link are equal to the current parameters.
      && ($variables['options']['query'] == $active['query']);
    
      // Add the "active" class if appropriate.
      if ($variables['url_is_active']) {
        $variables['options']['attributes']['class'][] = 'active';
      }
    
      // Remove all HTML and PHP tags from a tooltip, calling expensive strip_tags()
      // only when a quick strpos() gives suspicion tags are present.
      if (isset($variables['options']['attributes']['title']) && strpos($variables['options']['attributes']['title'], '<') !== FALSE) {
        $variables['options']['attributes']['title'] = strip_tags($variables['options']['attributes']['title']);
      }
    
      // Allow other modules to modify the structure of the link.
      Drupal::moduleHandler()->alter('link', $variables);
    
      // Move attributes out of options. url() doesn't need them.
      $attributes = new Attribute($variables['options']['attributes']);
      unset($variables['options']['attributes']);
    
      // The result of url() is a plain-text URL. Because we are using it here
      // in an HTML argument context, we need to encode it properly.
      $url = check_plain(url($variables['path'], $variables['options']));
    
      // Sanitize the link text if necessary.
      $text = $variables['options']['html'] ? $variables['text'] : check_plain($variables['text']);
    
      return '<a href="' . $url . '"' . $attributes . '>' . $text . '</a>';
    }
    
    /**
     * Forms an associative array from a linear array.
     *
     * @see \Drupal\Component\Utility\MapArray::copyValuesToKeys()
     */
    function drupal_map_assoc($array, $callable = NULL) {
      return MapArray::copyValuesToKeys($array, $callable);
    }
    
    /**
     * Attempts to set the PHP maximum execution time.
     *
     * This function is a wrapper around the PHP function set_time_limit().
     * When called, set_time_limit() restarts the timeout counter from zero.
     * In other words, if the timeout is the default 30 seconds, and 25 seconds
     * into script execution a call such as set_time_limit(20) is made, the
     * script will run for a total of 45 seconds before timing out.
     *
     * It also means that it is possible to decrease the total time limit if
     * the sum of the new time limit and the current time spent running the
     * script is inferior to the original time limit. It is inherent to the way
     * set_time_limit() works, it should rather be called with an appropriate
     * value every time you need to allocate a certain amount of time
     * to execute a task than only once at the beginning of the script.
     *
     * Before calling set_time_limit(), we check if this function is available
     * because it could be disabled by the server administrator. We also hide all
     * the errors that could occur when calling set_time_limit(), because it is
     * not possible to reliably ensure that PHP or a security extension will
     * not issue a warning/error if they prevent the use of this function.
     *
     * @param $time_limit
     *   An integer specifying the new time limit, in seconds. A value of 0
     *   indicates unlimited execution time.
     *
     * @ingroup php_wrappers
     */
    function drupal_set_time_limit($time_limit) {
      if (function_exists('set_time_limit')) {
        @set_time_limit($time_limit);
      }
    }
    
    /**
     * Returns the path to a system item (module, theme, etc.).
     *
     * @param $type
     *   The type of the item (i.e. theme, theme_engine, module, profile).
     * @param $name
     *   The name of the item for which the path is requested.
     *
     * @return
     *   The path to the requested item or an empty string if the item is not found.
     */
    function drupal_get_path($type, $name) {
      return dirname(drupal_get_filename($type, $name));
    }
    
    /**
     * Returns the base URL path (i.e., directory) of the Drupal installation.
     *
     * base_path() adds a "/" to the beginning and end of the returned path if the
     * path is not empty. At the very least, this will return "/".
     *
     * Examples:
     * - http://example.com returns "/" because the path is empty.
     * - http://example.com/drupal/folder returns "/drupal/folder/".
     */
    function base_path() {
      return $GLOBALS['base_path'];
    }
    
    /**
     * Adds a LINK tag with a distinct 'rel' attribute to the page's HEAD.
     *
     * This function can be called as long the HTML header hasn't been sent, which
     * on normal pages is up through the preprocess step of theme('html'). Adding
     * a link will overwrite a prior link with the exact same 'rel' and 'href'
     * attributes.
     *
     * @param $attributes
     *   Associative array of element attributes including 'href' and 'rel'.
     * @param $header
     *   Optional flag to determine if a HTTP 'Link:' header should be sent.
     */
    function drupal_add_html_head_link($attributes, $header = FALSE) {
      $element = array(
        '#tag' => 'link',
        '#attributes' => $attributes,
      );
      $href = $attributes['href'];
    
      if ($header) {
        // Also add a HTTP header "Link:".
        $href = '<' . check_plain($attributes['href']) . '>;';
        unset($attributes['href']);
        $element['#attached']['drupal_add_http_header'][] = array('Link',  $href . drupal_http_header_attributes($attributes), TRUE);
      }
    
      drupal_add_html_head($element, 'drupal_add_html_head_link:' . $attributes['rel'] . ':' . $href);
    }
    
    /**
     * Adds a cascading stylesheet to the stylesheet queue.
     *
     * Calling drupal_static_reset('drupal_add_css') will clear all cascading
     * stylesheets added so far.
     *
     * If CSS aggregation/compression is enabled, all cascading style sheets added
     * with $options['preprocess'] set to TRUE will be merged into one aggregate
     * file and compressed by removing all extraneous white space.
     * Preprocessed inline stylesheets will not be aggregated into this single file;
     * instead, they are just compressed upon output on the page. Externally hosted
     * stylesheets are never aggregated or compressed.
     *
     * The reason for aggregating the files is outlined quite thoroughly here:
     * http://www.die.net/musings/page_load_time/ "Load fewer external objects. Due
     * to request overhead, one bigger file just loads faster than two smaller ones
     * half its size."
     *
     * $options['preprocess'] should be only set to TRUE when a file is required for
     * all typical visitors and most pages of a site. It is critical that all
     * preprocessed files are added unconditionally on every page, even if the
     * files do not happen to be needed on a page. This is normally done by calling
     * drupal_add_css() in a hook_page_build() implementation.
     *
     * Non-preprocessed files should only be added to the page when they are
     * actually needed.
     *
     * @param $data
     *   (optional) The stylesheet data to be added, depending on what is passed
     *   through to the $options['type'] parameter:
     *   - 'file': The path to the CSS file relative to the base_path(), or a
     *     stream wrapper URI. For example: "modules/devel/devel.css" or
     *     "public://generated_css/stylesheet_1.css". Note that Modules should
     *     always prefix the names of their CSS files with the module name; for
     *     example, system-menus.css rather than simply menus.css. Themes can
     *     override module-supplied CSS files based on their filenames, and this
     *     prefixing helps prevent confusing name collisions for theme developers.
     *     See drupal_get_css() where the overrides are performed. Also, if the
     *     direction of the current language is right-to-left (Hebrew, Arabic,
     *     etc.), the function will also look for an RTL CSS file and append it to
     *     the list. The name of this file should have an '-rtl.css' suffix. For
     *     example, a CSS file called 'mymodule-name.css' will have a
     *     'mymodule-name-rtl.css' file added to the list, if exists in the same
     *     directory. This CSS file should contain overrides for properties which
     *     should be reversed or otherwise different in a right-to-left display.
     *   - 'inline': A string of CSS that should be placed in the given scope. Note
     *     that it is better practice to use 'file' stylesheets, rather than
     *     'inline', as the CSS would then be aggregated and cached.
     *   - 'external': The absolute path to an external CSS file that is not hosted
     *     on the local server. These files will not be aggregated if CSS
     *     aggregation is enabled.
     * @param $options
     *   (optional) A string defining the 'type' of CSS that is being added in the
     *   $data parameter ('file', 'inline', or 'external'), or an array which can
     *   have any or all of the following keys:
     *   - 'type': The type of stylesheet being added. Available options are 'file',
     *     'inline' or 'external'. Defaults to 'file'.
     *   - 'basename': Force a basename for the file being added. Modules are
     *     expected to use stylesheets with unique filenames, but integration of
     *     external libraries may make this impossible. The basename of
     *     'core/modules/node/node.css' is 'node.css'. If the external library
     *     "node.js" ships with a 'node.css', then a different, unique basename
     *     would be 'node.js.css'.
     *   - 'group': A number identifying the aggregation group in which to add the
     *     stylesheet. Available constants are:
     *     - CSS_AGGREGATE_DEFAULT: (default) Any module-layer CSS.
     *     - CSS_AGGREGATE_THEME: Any theme-layer CSS.
     *     The aggregate group number affects load order and the CSS cascade.
     *     Stylesheets in an aggregate with a lower group number will be output to
     *     the page before stylesheets in an aggregate with a higher group number,
     *     so CSS within higher aggregate groups can take precendence over CSS
     *     within lower aggregate groups.
     *   - 'every_page': For optimal front-end performance when aggregation is
     *     enabled, this should be set to TRUE if the stylesheet is present on every
     *     page of the website for users for whom it is present at all. This
     *     defaults to FALSE. It is set to TRUE for stylesheets added via module and
     *     theme .info.yml files. Modules that add stylesheets within
     *     hook_page_build() implementations, or from other code that ensures that
     *     the stylesheet is added to all website pages, should also set this flag
     *     to TRUE. All stylesheets within the same group that have the 'every_page'
     *     flag set to TRUE and do not have 'preprocess' set to FALSE are aggregated
     *     together into a single aggregate file, and that aggregate file can be
     *     reused across a user's entire site visit, leading to faster navigation
     *     between pages.
     *     However, stylesheets that are only needed on pages less frequently
     *     visited, can be added by code that only runs for those particular pages,
     *     and that code should not set the 'every_page' flag. This minimizes the
     *     size of the aggregate file that the user needs to download when first
     *     visiting the website. Stylesheets without the 'every_page' flag are
     *     aggregated into a separate aggregate file. This other aggregate file is
     *     likely to change from page to page, and each new aggregate file needs to
     *     be downloaded when first encountered, so it should be kept relatively
     *     small by ensuring that most commonly needed stylesheets are added to
     *     every page.
     *   - 'weight': The weight of the stylesheet specifies the order in which the
     *     CSS will appear relative to other stylesheets with the same aggregate
     *     group and 'every_page' flag. The exact ordering of stylesheets is as
     *     follows:
     *     - First by aggregate group.
     *     - Then by the 'every_page' flag, with TRUE coming before FALSE.
     *     - Then by weight.
     *     - Then by the order in which the CSS was added. For example, all else
     *       being the same, a stylesheet added by a call to drupal_add_css() that
     *       happened later in the page request gets added to the page after one for
     *       which drupal_add_css() happened earlier in the page request.
     *     Available constants are:
     *     - CSS_BASE: Styles for HTML elements ("base" styles).
     *     - CSS_LAYOUT: Styles that layout a page.
     *     - CSS_COMPONENT: Styles for design components (and their associated
     *       states and skins.)
     *     - CSS_STATE: Styles for states that are not included with components.
     *     - CSS_SKIN: Styles for skins that are not included with components.
     *     The weight numbers follow the SMACSS convention of CSS categorization.
     *     See http://drupal.org/node/1887922
     *   - 'media': The media type for the stylesheet, e.g., all, print, screen.
     *     Defaults to 'all'. It is extremely important to leave this set to 'all'
     *     or it will negatively impact front-end peformance. Instead add a @media
     *     block to the included CSS file.
     *   - 'preprocess': If TRUE and CSS aggregation/compression is enabled, the
     *     styles will be aggregated and compressed. Defaults to TRUE.
     *   - 'browsers': An array containing information specifying which browsers
     *     should load the CSS item. See drupal_pre_render_conditional_comments()
     *     for details.
     *
     * @return
     *   An array of queued cascading stylesheets.
     *
     * @deprecated as of Drupal 8.0. Use the #attached key in render arrays instead.
     *
     * @see drupal_get_css()
     */
    function drupal_add_css($data = NULL, $options = NULL) {
      $css = &drupal_static(__FUNCTION__, array());
    
      // Construct the options, taking the defaults into consideration.
      if (isset($options)) {
        if (!is_array($options)) {
          $options = array('type' => $options);
        }
      }
      else {
        $options = array();
      }
    
      // Create an array of CSS files for each media type first, since each type needs to be served
      // to the browser differently.
      if (isset($data)) {
        $options += array(
          'type' => 'file',
          'group' => CSS_AGGREGATE_DEFAULT,
          'weight' => 0,
          'every_page' => FALSE,
          'media' => 'all',
          'preprocess' => TRUE,
          'data' => $data,
          'browsers' => array(),
        );
        $options['browsers'] += array(
          'IE' => TRUE,
          '!IE' => TRUE,
        );
    
        // Files with a query string cannot be preprocessed.
        if ($options['type'] === 'file' && $options['preprocess'] && strpos($options['data'], '?') !== FALSE) {
          $options['preprocess'] = FALSE;
        }
    
        // Always add a tiny value to the weight, to conserve the insertion order.
        $options['weight'] += count($css) / 1000;
    
        // Add the data to the CSS array depending on the type.
        switch ($options['type']) {
          case 'inline':
            // For inline stylesheets, we don't want to use the $data as the array
            // key as $data could be a very long string of CSS.
            $css[] = $options;
            break;
    
          case 'file':
            // Local CSS files are keyed by basename; if a file with the same
            // basename is added more than once, it gets overridden.
            // By default, take over the filename as basename.
            if (!isset($options['basename'])) {
              $options['basename'] = drupal_basename($data);
            }
            $css[$options['basename']] = $options;
            break;
    
          default:
            // External files are keyed by their full URI, so the same CSS file is
            // not added twice.
            $css[$data] = $options;
        }
      }
    
      return $css;
    }
    
    /**
     * Returns a themed representation of all stylesheets to attach to the page.
     *
     * It loads the CSS in order, with 'module' first, then 'theme' afterwards.
     * This ensures proper cascading of styles so themes can easily override
     * module styles through CSS selectors.
     *
     * Themes may replace module-defined CSS files by adding a stylesheet with the
     * same filename. For example, themes/bartik/system-menus.css would replace
     * modules/system/system-menus.css. This allows themes to override complete
     * CSS files, rather than specific selectors, when necessary.
     *
     * If the original CSS file is being overridden by a theme, the theme is
     * responsible for supplying an accompanying RTL CSS file to replace the
     * module's.
     *
     * @param $css
     *   (optional) An array of CSS files. If no array is provided, the default
     *   stylesheets array is used instead.
     * @param $skip_alter
     *   (optional) If set to TRUE, this function skips calling drupal_alter() on
     *   $css, useful when the calling function passes a $css array that has already
     *   been altered.
     *
     * @return
     *   A string of XHTML CSS tags.
     *
     * @see drupal_add_css()
     */
    function drupal_get_css($css = NULL, $skip_alter = FALSE) {
      global $theme_info;
    
      if (!isset($css)) {
        $css = drupal_add_css();
      }
    
      // Allow modules and themes to alter the CSS items.
      if (!$skip_alter) {
        drupal_alter('css', $css);
      }
    
      // Sort CSS items, so that they appear in the correct order.
      uasort($css, 'drupal_sort_css_js');
    
      // Allow themes to remove CSS files by basename.
      if (!empty($theme_info->stylesheets_remove)) {
        foreach ($css as $key => $options) {
          if (isset($options['basename']) && isset($theme_info->stylesheets_remove[$options['basename']])) {
            unset($css[$key]);
          }
        }
      }
      // Allow themes to conditionally override CSS files by basename.
      if (!empty($theme_info->stylesheets_override)) {
        foreach ($css as $key => $options) {
          if (isset($options['basename']) && isset($theme_info->stylesheets_override[$options['basename']])) {
            $css[$key]['data'] = $theme_info->stylesheets_override[$options['basename']];
          }
        }
      }
    
      // Render the HTML needed to load the CSS.
      $styles = array(
        '#type' => 'styles',
        '#items' => $css,
      );
      if (!empty($setting)) {
        $styles['#attached']['js'][] = array('type' => 'setting', 'data' => $setting);
      }
    
      return drupal_render($styles);
    }
    
    /**
     * Sorts CSS and JavaScript resources.
     *
     * Callback for uasort() within:
     * - drupal_get_css()
     * - drupal_get_js()
     *
     * This sort order helps optimize front-end performance while providing modules
     * and themes with the necessary control for ordering the CSS and JavaScript
     * appearing on a page.
     *
     * @param $a
     *   First item for comparison. The compared items should be associative arrays
     *   of member items from drupal_add_css() or drupal_add_js().
     * @param $b
     *   Second item for comparison.
     *
     * @see drupal_add_css()
     * @see drupal_add_js()
     */
    function drupal_sort_css_js($a, $b) {
      // First order by group, so that all items in the CSS_AGGREGATE_DEFAULT group
      // appear before items in the CSS_AGGREGATE_THEME group. Modules may create
      // additional groups by defining their own constants.
      if ($a['group'] < $b['group']) {
        return -1;
      }
      elseif ($a['group'] > $b['group']) {
        return 1;
      }
      // Within a group, order all infrequently needed, page-specific files after
      // common files needed throughout the website. Separating this way allows for
      // the aggregate file generated for all of the common files to be reused
      // across a site visit without being cut by a page using a less common file.
      elseif ($a['every_page'] && !$b['every_page']) {
        return -1;
      }
      elseif (!$a['every_page'] && $b['every_page']) {
        return 1;
      }
      // Finally, order by weight.
      elseif ($a['weight'] < $b['weight']) {
        return -1;
      }
      elseif ($a['weight'] > $b['weight']) {
        return 1;
      }
      else {
        return 0;
      }
    }
    
    /**
     * Pre-render callback: Adds the elements needed for CSS tags to be rendered.
     *
     * For production websites, LINK tags are preferable to STYLE tags with @import
     * statements, because:
     * - They are the standard tag intended for linking to a resource.
     * - On Firefox 2 and perhaps other browsers, CSS files included with @import
     *   statements don't get saved when saving the complete web page for offline
     *   use: http://drupal.org/node/145218.
     * - On IE, if only LINK tags and no @import statements are used, all the CSS
     *   files are downloaded in parallel, resulting in faster page load, but if
     *   @import statements are used and span across multiple STYLE tags, all the
     *   ones from one STYLE tag must be downloaded before downloading begins for
     *   the next STYLE tag. Furthermore, IE7 does not support media declaration on
     *   the @import statement, so multiple STYLE tags must be used when different
     *   files are for different media types. Non-IE browsers always download in
     *   parallel, so this is an IE-specific performance quirk:
     *   http://www.stevesouders.com/blog/2009/04/09/dont-use-import/.
     *
     * However, IE has an annoying limit of 31 total CSS inclusion tags
     * (http://drupal.org/node/228818) and LINK tags are limited to one file per
     * tag, whereas STYLE tags can contain multiple @import statements allowing
     * multiple files to be loaded per tag. When CSS aggregation is disabled, a
     * Drupal site can easily have more than 31 CSS files that need to be loaded, so
     * using LINK tags exclusively would result in a site that would display
     * incorrectly in IE. Depending on different needs, different strategies can be
     * employed to decide when to use LINK tags and when to use STYLE tags.
     *
     * The strategy employed by this function is to use LINK tags for all aggregate
     * files and for all files that cannot be aggregated (e.g., if 'preprocess' is
     * set to FALSE or the type is 'external'), and to use STYLE tags for groups
     * of files that could be aggregated together but aren't (e.g., if the site-wide
     * aggregation setting is disabled). This results in all LINK tags when
     * aggregation is enabled, a guarantee that as many or only slightly more tags
     * are used with aggregation disabled than enabled (so that if the limit were to
     * be crossed with aggregation enabled, the site developer would also notice the
     * problem while aggregation is disabled), and an easy way for a developer to
     * view HTML source while aggregation is disabled and know what files will be
     * aggregated together when aggregation becomes enabled.
     *
     * This function evaluates the aggregation enabled/disabled condition on a group
     * by group basis by testing whether an aggregate file has been made for the
     * group rather than by testing the site-wide aggregation setting. This allows
     * this function to work correctly even if modules have implemented custom
     * logic for grouping and aggregating files.
     *
     * @param $element
     *   A render array containing:
     *   - '#items': The CSS items as returned by drupal_add_css() and altered by
     *     drupal_get_css().
     *
     * @return
     *   A render array that will render to a string of XHTML CSS tags.
     *
     * @see drupal_get_css()
     */
    function drupal_pre_render_styles($elements) {
      $css_assets = $elements['#items'];
    
      // Aggregate the CSS if necessary, but only during normal site operation.
      if (!defined('MAINTENANCE_MODE') && Drupal::config('system.performance')->get('css.preprocess')) {
        $css_assets = \Drupal::service('asset.css.collection_optimizer')->optimize($css_assets);
      }
      return \Drupal::service('asset.css.collection_renderer')->render($css_assets);
    }
    
    /**
     * Deletes old cached CSS files.
     */
    function drupal_clear_css_cache() {
      Drupal::state()->delete('drupal_css_cache_files');
      file_scan_directory('public://css', '/.*/', array('callback' => 'drupal_delete_file_if_stale'));
    }
    
    /**
     * Deletes files modified more than a set time ago.
     *
     * Callback for file_scan_directory() within:
     * - drupal_clear_css_cache()
     * - drupal_clear_js_cache()
     */
    function drupal_delete_file_if_stale($uri) {
      // Default stale file threshold is 30 days.
      if (REQUEST_TIME - filemtime($uri) > Drupal::config('system.performance')->get('stale_file_threshold')) {
        file_unmanaged_delete($uri);
      }
    }
    
    /**
     * Prepares a string for use as a CSS identifier (element, class, or ID name).
     *
     * http://www.w3.org/TR/CSS21/syndata.html#characters shows the syntax for valid
     * CSS identifiers (including element names, classes, and IDs in selectors.)
     *
     * @param $identifier
     *   The identifier to clean.
     * @param $filter
     *   An array of string replacements to use on the identifier.
     *
     * @return
     *   The cleaned identifier.
     */
    function drupal_clean_css_identifier($identifier, $filter = array(' ' => '-', '_' => '-', '__' => '__', '/' => '-', '[' => '-', ']' => '')) {
      // By default, we filter using Drupal's coding standards.
      $identifier = strtr($identifier, $filter);
    
      // Valid characters in a CSS identifier are:
      // - the hyphen (U+002D)
      // - a-z (U+0030 - U+0039)
      // - A-Z (U+0041 - U+005A)
      // - the underscore (U+005F)
      // - 0-9 (U+0061 - U+007A)
      // - ISO 10646 characters U+00A1 and higher
      // We strip out any character not in the above list.
      $identifier = preg_replace('/[^\x{002D}\x{0030}-\x{0039}\x{0041}-\x{005A}\x{005F}\x{0061}-\x{007A}\x{00A1}-\x{FFFF}]/u', '', $identifier);
    
      return $identifier;
    }
    
    /**
     * Prepares a string for use as a valid class name.
     *
     * Do not pass one string containing multiple classes as they will be
     * incorrectly concatenated with dashes, i.e. "one two" will become "one-two".
     *
     * @param $class
     *   The class name to clean.
     *
     * @return
     *   The cleaned class name.
     */
    function drupal_html_class($class) {
      // The output of this function will never change, so this uses a normal
      // static instead of drupal_static().
      static $classes = array();
    
      if (!isset($classes[$class])) {
        $classes[$class] = drupal_clean_css_identifier(drupal_strtolower($class));
      }
      return $classes[$class];
    }
    
    /**
     * Prepares a string for use as a valid HTML ID and guarantees uniqueness.
     *
     * This function ensures that each passed HTML ID value only exists once on the
     * page. By tracking the already returned ids, this function enables forms,
     * blocks, and other content to be output multiple times on the same page,
     * without breaking (X)HTML validation.
     *
     * For already existing IDs, a counter is appended to the ID string. Therefore,
     * JavaScript and CSS code should not rely on any value that was generated by
     * this function and instead should rely on manually added CSS classes or
     * similarly reliable constructs.
     *
     * Two consecutive hyphens separate the counter from the original ID. To manage
     * uniqueness across multiple Ajax requests on the same page, Ajax requests
     * POST an array of all IDs currently present on the page, which are used to
     * prime this function's cache upon first invocation.
     *
     * To allow reverse-parsing of IDs submitted via Ajax, any multiple consecutive
     * hyphens in the originally passed $id are replaced with a single hyphen.
     *
     * @param $id
     *   The ID to clean.
     *
     * @return
     *   The cleaned ID.
     */
    function drupal_html_id($id) {
      // If this is an Ajax request, then content returned by this page request will
      // be merged with content already on the base page. The HTML IDs must be
      // unique for the fully merged content. Therefore, initialize $seen_ids to
      // take into account IDs that are already in use on the base page.
      $seen_ids_init = &drupal_static(__FUNCTION__ . ':init');
      if (!isset($seen_ids_init)) {
        // Ideally, Drupal would provide an API to persist state information about
        // prior page requests in the database, and we'd be able to add this
        // function's $seen_ids static variable to that state information in order
        // to have it properly initialized for this page request. However, no such
        // page state API exists, so instead, ajax.js adds all of the in-use HTML
        // IDs to the POST data of Ajax submissions. Direct use of $_POST is
        // normally not recommended as it could open up security risks, but because
        // the raw POST data is cast to a number before being returned by this
        // function, this usage is safe.
        if (empty($_POST['ajax_html_ids'])) {
          $seen_ids_init = array();
        }
        else {
          // This function ensures uniqueness by appending a counter to the base id
          // requested by the calling function after the first occurrence of that
          // requested id. $_POST['ajax_html_ids'] contains the ids as they were
          // returned by this function, potentially with the appended counter, so
          // we parse that to reconstruct the $seen_ids array.
          $ajax_html_ids = explode(' ', $_POST['ajax_html_ids']);
          foreach ($ajax_html_ids as $seen_id) {
            // We rely on '--' being used solely for separating a base id from the
            // counter, which this function ensures when returning an id.
            $parts = explode('--', $seen_id, 2);
            if (!empty($parts[1]) && is_numeric($parts[1])) {
              list($seen_id, $i) = $parts;
            }
            else {
              $i = 1;
            }
            if (!isset($seen_ids_init[$seen_id]) || ($i > $seen_ids_init[$seen_id])) {
              $seen_ids_init[$seen_id] = $i;
            }
          }
        }
      }
      $seen_ids = &drupal_static(__FUNCTION__, $seen_ids_init);
    
      $id = strtr(drupal_strtolower($id), array(' ' => '-', '_' => '-', '[' => '-', ']' => ''));
    
      // As defined in http://www.w3.org/TR/html4/types.html#type-name, HTML IDs can
      // only contain letters, digits ([0-9]), hyphens ("-"), underscores ("_"),
      // colons (":"), and periods ("."). We strip out any character not in that
      // list. Note that the CSS spec doesn't allow colons or periods in identifiers
      // (http://www.w3.org/TR/CSS21/syndata.html#characters), so we strip those two
      // characters as well.
      $id = preg_replace('/[^A-Za-z0-9\-_]/', '', $id);
    
      // Removing multiple consecutive hyphens.
      $id = preg_replace('/\-+/', '-', $id);
      // Ensure IDs are unique by appending a counter after the first occurrence.
      // The counter needs to be appended with a delimiter that does not exist in
      // the base ID. Requiring a unique delimiter helps ensure that we really do
      // return unique IDs and also helps us re-create the $seen_ids array during
      // Ajax requests.
      if (isset($seen_ids[$id])) {
        $id = $id . '--' . ++$seen_ids[$id];
      }
      else {
        $seen_ids[$id] = 1;
      }
    
      return $id;
    }
    
    /**
     * Adds a JavaScript file, setting, or inline code to the page.
     *
     * The behavior of this function depends on the parameters it is called with.
     * Generally, it handles the addition of JavaScript to the page, either as
     * reference to an existing file or as inline code. The following actions can be
     * performed using this function:
     * - Add a file ('file'): Adds a reference to a JavaScript file to the page.
     * - Add inline JavaScript code ('inline'): Executes a piece of JavaScript code
     *   on the current page by placing the code directly in the page (for example,
     *   to tell the user that a new message arrived, by opening a pop up, alert
     *   box, etc.). This should only be used for JavaScript that cannot be executed
     *   from a file. When adding inline code, make sure that you are not relying on
     *   $() being the jQuery function. Wrap your code in
     *   @code (function ($) {... })(jQuery); @endcode
     *   or use jQuery() instead of $().
     * - Add external JavaScript ('external'): Allows the inclusion of external
     *   JavaScript files that are not hosted on the local server. Note that these
     *   external JavaScript references do not get aggregated when preprocessing is
     *   on.
     * - Add settings ('setting'): Adds settings to Drupal's global storage of
     *   JavaScript settings. Per-page settings are required by some modules to
     *   function properly. All settings will be accessible at Drupal.settings.
     *
     * Examples:
     * @code
     *   drupal_add_js('core/misc/collapse.js');
     *   drupal_add_js('core/misc/collapse.js', 'file');
     *   drupal_add_js('jQuery(document).ready(function () { alert("Hello!"); });', 'inline');
     *   drupal_add_js('jQuery(document).ready(function () { alert("Hello!"); });',
     *     array('type' => 'inline', 'scope' => 'footer', 'weight' => 5)
     *   );
     *   drupal_add_js('http://example.com/example.js', 'external');
     *   drupal_add_js(array('myModule' => array('key' => 'value')), 'setting');
     * @endcode
     *
     * Calling drupal_static_reset('drupal_add_js') will clear all JavaScript added
     * so far.
     *
     * If JavaScript aggregation is enabled, all JavaScript files added with
     * $options['preprocess'] set to TRUE will be merged into one aggregate file.
     * Preprocessed inline JavaScript will not be aggregated into this single file.
     * Externally hosted JavaScripts are never aggregated.
     *
     * The reason for aggregating the files is outlined quite thoroughly here:
     * http://www.die.net/musings/page_load_time/ "Load fewer external objects. Due
     * to request overhead, one bigger file just loads faster than two smaller ones
     * half its size."
     *
     * $options['preprocess'] should be only set to TRUE when a file is required for
     * all typical visitors and most pages of a site. It is critical that all
     * preprocessed files are added unconditionally on every page, even if the
     * files are not needed on a page. This is normally done by calling
     * drupal_add_js() in a hook_page_build() implementation.
     *
     * Non-preprocessed files should only be added to the page when they are
     * actually needed.
     *
     * @param $data
     *   (optional) If given, the value depends on the $options parameter, or
     *   $options['type'] if $options is passed as an associative array:
     *   - 'file': Path to the file relative to base_path().
     *   - 'inline': The JavaScript code that should be placed in the given scope.
     *   - 'external': The absolute path to an external JavaScript file that is not
     *     hosted on the local server. These files will not be aggregated if
     *     JavaScript aggregation is enabled.
     *   - 'setting': An associative array with configuration options. The array is
     *     merged directly into Drupal.settings. All modules should wrap their
     *     actual configuration settings in another variable to prevent conflicts in
     *     the Drupal.settings namespace. Items added with a string key will replace
     *     existing settings with that key; items with numeric array keys will be
     *     added to the existing settings array.
     * @param $options
     *   (optional) A string defining the type of JavaScript that is being added in
     *   the $data parameter ('file'/'setting'/'inline'/'external'), or an
     *   associative array. JavaScript settings should always pass the string
     *   'setting' only. Other types can have the following elements in the array:
     *   - type: The type of JavaScript that is to be added to the page. Allowed
     *     values are 'file', 'inline', 'external' or 'setting'. Defaults
     *     to 'file'.
     *   - scope: The location in which you want to place the script. Possible
     *     values are 'header' or 'footer'. If your theme implements different
     *     regions, you can also use these. Defaults to 'header'.
     *   - group: A number identifying the group in which to add the JavaScript.
     *     Available constants are:
     *     - JS_LIBRARY: Any libraries, settings, or jQuery plugins.
     *     - JS_DEFAULT: Any module-layer JavaScript.
     *     - JS_THEME: Any theme-layer JavaScript.
     *     The group number serves as a weight: JavaScript within a lower weight
     *     group is presented on the page before JavaScript within a higher weight
     *     group.
     *   - every_page: For optimal front-end performance when aggregation is
     *     enabled, this should be set to TRUE if the JavaScript is present on every
     *     page of the website for users for whom it is present at all. This
     *     defaults to FALSE. It is set to TRUE for JavaScript files that are added
     *     via module and theme .info.yml files. Modules that add JavaScript within
     *     hook_page_build() implementations, or from other code that ensures that
     *     the JavaScript is added to all website pages, should also set this flag
     *     to TRUE. All JavaScript files within the same group and that have the
     *     'every_page' flag set to TRUE and do not have 'preprocess' set to FALSE
     *     are aggregated together into a single aggregate file, and that aggregate
     *     file can be reused across a user's entire site visit, leading to faster
     *     navigation between pages. However, JavaScript that is only needed on
     *     pages less frequently visited, can be added by code that only runs for
     *     those particular pages, and that code should not set the 'every_page'
     *     flag. This minimizes the size of the aggregate file that the user needs
     *     to download when first visiting the website. JavaScript without the
     *     'every_page' flag is aggregated into a separate aggregate file. This
     *     other aggregate file is likely to change from page to page, and each new
     *     aggregate file needs to be downloaded when first encountered, so it
     *     should be kept relatively small by ensuring that most commonly needed
     *     JavaScript is added to every page.
     *   - weight: A number defining the order in which the JavaScript is added to
     *     the page relative to other JavaScript with the same 'scope', 'group',
     *     and 'every_page' value. In some cases, the order in which the JavaScript
     *     is presented on the page is very important. jQuery, for example, must be
     *     added to the page before any jQuery code is run, so jquery.js uses the
     *     JS_LIBRARY group and a weight of -20, jquery.once.js (a library drupal.js
     *     depends on) uses the JS_LIBRARY group and a weight of -19, drupal.js uses
     *     the JS_LIBRARY group and a weight of -1, other libraries use the
     *     JS_LIBRARY group and a weight of 0 or higher, and all other scripts use
     *     one of the other group constants. The exact ordering of JavaScript is as
     *     follows:
     *     - First by scope, with 'header' first, 'footer' last, and any other
     *       scopes provided by a custom theme coming in between, as determined by
     *       the theme.
     *     - Then by group.
     *     - Then by the 'every_page' flag, with TRUE coming before FALSE.
     *     - Then by weight.
     *     - Then by the order in which the JavaScript was added. For example, all
     *       else being the same, JavaScript added by a call to drupal_add_js() that
     *       happened later in the page request gets added to the page after one for
     *       which drupal_add_js() happened earlier in the page request.
     *   - cache: If set to FALSE, the JavaScript file is loaded anew on every page
     *     call; in other words, it is not cached. Used only when 'type' references
     *     a JavaScript file. Defaults to TRUE.
     *   - preprocess: If TRUE and JavaScript aggregation is enabled, the script
     *     file will be aggregated. Defaults to TRUE.
     *   - attributes: An associative array of attributes for the <script> tag. This
     *     may be used to add 'defer', 'async', or custom attributes. Note that
     *     setting any attributes will disable preprocessing as though the
     *     'preprocess' option was set to FALSE.
     *   - browsers: An array containing information specifying which browsers
     *     should load the JavaScript item. See
     *     drupal_pre_render_conditional_comments() for details.
     *
     * @return
     *   The current array of JavaScript files, settings, and in-line code,
     *   including Drupal defaults, anything previously added with calls to
     *   drupal_add_js(), and this function call's additions.
     *
     * @deprecated as of Drupal 8.0. Use the #attached key in render arrays instead.
     *
     * @see drupal_get_js()
     */
    function drupal_add_js($data = NULL, $options = NULL) {
      $javascript = &drupal_static(__FUNCTION__, array());
    
      // Construct the options, taking the defaults into consideration.
      if (isset($options)) {
        if (!is_array($options)) {
          $options = array('type' => $options);
        }
      }
      else {
        $options = array();
      }
      $options += drupal_js_defaults($data);
    
      // Preprocess can only be set if caching is enabled and no attributes are set.
      $options['preprocess'] = $options['cache'] && empty($options['attributes']) ? $options['preprocess'] : FALSE;
    
      // Tweak the weight so that files of the same weight are included in the
      // order of the calls to drupal_add_js().
      $options['weight'] += count($javascript) / 1000;
      if (isset($data)) {
        switch ($options['type']) {
          case 'setting':
            // If the setting array doesn't exist, add defaults values.
            if (!isset($javascript['settings'])) {
              $javascript['settings'] = array(
                'type' => 'setting',
                'scope' => 'header',
                'group' => JS_SETTING,
                'every_page' => TRUE,
                'weight' => 0,
                'browsers' => array(),
              );
              // url() generates the script and prefix using hook_url_outbound_alter().
              // Instead of running the hook_url_outbound_alter() again here, extract
              // them from url().
              // @todo Make this less hacky: http://drupal.org/node/1547376.
              $scriptPath = $GLOBALS['script_path'];
              $pathPrefix = '';
              url('', array('script' => &$scriptPath, 'prefix' => &$pathPrefix));
              $javascript['settings']['data'][] = array(
                'basePath' => base_path(),
                'scriptPath' => $scriptPath,
                'pathPrefix' => $pathPrefix,
                'currentPath' => current_path(),
              );
            }
            // All JavaScript settings are placed in the header of the page with
            // the library weight so that inline scripts appear afterwards.
            $javascript['settings']['data'][] = $data;
            break;
    
          case 'inline':
            $javascript[] = $options;
            break;
    
          default: // 'file' and 'external'
            // Local and external files must keep their name as the associative key
            // so the same JavaScript file is not added twice.
            $javascript[$options['data']] = $options;
        }
      }
      return $javascript;
    }
    
    /**
     * Constructs an array of the defaults that are used for JavaScript items.
     *
     * @param $data
     *   (optional) The default data parameter for the JavaScript item array.
     *
     * @see drupal_get_js()
     * @see drupal_add_js()
     */
    function drupal_js_defaults($data = NULL) {
      return array(
        'type' => 'file',
        'group' => JS_DEFAULT,
        'every_page' => FALSE,
        'weight' => 0,
        'scope' => 'header',
        'cache' => TRUE,
        'preprocess' => TRUE,
        'attributes' => array(),
        'version' => NULL,
        'data' => $data,
        'browsers' => array(),
      );
    }
    
    /**
     * Returns a themed presentation of all JavaScript code for the current page.
     *
     * References to JavaScript files are placed in a certain order: first, all
     * 'core' files, then all 'module' and finally all 'theme' JavaScript files
     * are added to the page. Then, all settings are output, followed by 'inline'
     * JavaScript code. If running update.php, all preprocessing is disabled.
     *
     * Note that hook_js_alter(&$javascript) is called during this function call
     * to allow alterations of the JavaScript during its presentation. Calls to
     * drupal_add_js() from hook_js_alter() will not be added to the output
     * presentation. The correct way to add JavaScript during hook_js_alter()
     * is to add another element to the $javascript array, deriving from
     * drupal_js_defaults(). See locale_js_alter() for an example of this.
     *
     * @param $scope
     *   (optional) The scope for which the JavaScript rules should be returned.
     *   Defaults to 'header'.
     * @param $javascript
     *   (optional) An array with all JavaScript code. Defaults to the default
     *   JavaScript array for the given scope.
     * @param bool $skip_alter
     *   (optional) If set to TRUE, this function skips calling drupal_alter() on
     *   $javascript, useful when the calling function passes a $javascript array
     *   that has already been altered.
     * @param bool $is_ajax
     *   (optional) If set to TRUE, this function is called from an Ajax request and
     *   adds javascript settings to update ajaxPageState values.
     *
     * @return
     *   All JavaScript code segments and includes for the scope as HTML tags.
     *
     * @see drupal_add_js()
     * @see locale_js_alter()
     * @see drupal_js_defaults()
     */
    function drupal_get_js($scope = 'header', $javascript = NULL, $skip_alter = FALSE, $is_ajax = FALSE) {
      if (!isset($javascript)) {
        $javascript = drupal_add_js();
      }
      if (empty($javascript)) {
        return '';
      }
    
      // Allow modules to alter the JavaScript.
      if (!$skip_alter) {
        drupal_alter('js', $javascript);
      }
    
      // Filter out elements of the given scope.
      $items = array();
      foreach ($javascript as $key => $item) {
        if ($item['scope'] == $scope) {
          $items[$key] = $item;
        }
      }
    
      if (!empty($items)) {
        // Sort the JavaScript files so that they appear in the correct order.
        uasort($items, 'drupal_sort_css_js');
        // Don't add settings if there is no other JavaScript on the page, unless
        // this is an AJAX request.
        if (!empty($items['settings']) || $is_ajax) {
          global $theme_key;
          // Provide the page with information about the theme that's used, so that
          // a later AJAX request can be rendered using the same theme.
          // @see ajax_base_page_theme()
          $setting['ajaxPageState']['theme'] = $theme_key;
          // Checks that the DB is available before filling theme_token.
          if (!defined('MAINTENANCE_MODE')) {
            $setting['ajaxPageState']['theme_token'] = drupal_get_token($theme_key);
          }
    
          // Provide the page with information about the individual JavaScript files
          // used, information not otherwise available when aggregation is enabled.
          $setting['ajaxPageState']['js'] = array_fill_keys(array_keys($javascript), 1);
          unset($setting['ajaxPageState']['js']['settings']);
    
          // Provide the page with information about the individual CSS files used,
          // information not otherwise available when CSS aggregation is enabled.
          // The setting is attached later in this function, but is set here, so
          // that CSS files removed in drupal_process_attached() are still
          // considered "used" and prevented from being added in a later AJAX
          // request.
          // Skip if no files were added to the page otherwise jQuery.extend() will
          // overwrite the Drupal.settings.ajaxPageState.css object with an empty
          // array.
          $css = drupal_add_css();
          if (!empty($css)) {
            // Cast the array to an object to be on the safe side even if not empty.
            $setting['ajaxPageState']['css'] = (object) array_fill_keys(array_keys($css), 1);
          }
    
          drupal_add_js($setting, 'setting');
    
          // If we're outputting the header scope, then this might be the final time
          // that drupal_get_js() is running, so add the settings to this output as well
          // as to the drupal_add_js() cache. If $items['settings'] doesn't exist, it's
          // because drupal_get_js() was intentionally passed a $javascript argument
          // stripped of settings, potentially in order to override how settings get
          // output, so in this case, do not add the setting to this output.
          if ($scope == 'header' && isset($items['settings'])) {
            $items['settings']['data'][] = $setting;
          }
        }
      }
    
      // Render the HTML needed to load the JavaScript.
      $elements = array(
        '#type' => 'scripts',
        '#items' => $items,
      );
    
      return drupal_render($elements);
    }
    
    /**
     * Merges an array of settings arrays into a single settings array.
     *
     * This function merges the items in the same way that
     *
     * @code
     *   jQuery.extend(true, {}, $settings_items[0], $settings_items[1], ...)
     * @endcode
     *
     * would. This means integer indices are preserved just like string indices are,
     * rather than re-indexed as is common in PHP array merging.
     *
     * Example:
     * @code
     * function module1_page_build(&$page) {
     *   $page['#attached']['js'][] = array(
     *     'type' => 'setting',
     *     'data' => array('foo' => array('a', 'b', 'c')),
     *   );
     * }
     * function module2_page_build(&$page) {
     *   $page['#attached']['js'][] = array(
     *     'type' => 'setting',
     *     'data' => array('foo' => array('d')),
     *   );
     * }
     * // When the page is rendered after the above code, and the browser runs the
     * // resulting <SCRIPT> tags, the value of drupalSettings.foo is
     * // ['d', 'b', 'c'], not ['a', 'b', 'c', 'd'].
     * @endcode
     *
     * By following jQuery.extend() merge logic rather than common PHP array merge
     * logic, the following are ensured:
     * - drupal_add_js() is idempotent: calling it twice with the same parameters
     *   does not change the output sent to the browser.
     * - If pieces of the page are rendered in separate PHP requests and the
     *   returned settings are merged by JavaScript, the resulting settings are the
     *   same as if rendered in one PHP request and merged by PHP.
     *
     * @param $settings_items
     *   An array of settings arrays, as returned by:
     *   @code
     *     $js = drupal_add_js();
     *     $settings_items = $js['settings']['data'];
     *   @endcode
     *
     * @return
     *   A merged $settings array, suitable for JSON encoding and returning to the
     *   browser.
     *
     * @see drupal_add_js()
     * @see drupal_pre_render_scripts()
     */
    function drupal_merge_js_settings($settings_items) {
      return NestedArray::mergeDeepArray($settings_items, TRUE);
    }
    
    /**
     * #pre_render callback to add the elements needed for JavaScript tags to be rendered.
     *
     * This function evaluates the aggregation enabled/disabled condition on a group
     * by group basis by testing whether an aggregate file has been made for the
     * group rather than by testing the site-wide aggregation setting. This allows
     * this function to work correctly even if modules have implemented custom
     * logic for grouping and aggregating files.
     *
     * @param $element
     *   A render array containing:
     *   - #items: The JavaScript items as returned by drupal_add_js() and
     *     altered by drupal_get_js().
     *   - #group_callback: A function to call to group #items. Following
     *     this function, #aggregate_callback is called to aggregate items within
     *     the same group into a single file.
     *   - #aggregate_callback: A function to call to aggregate the items within
     *     the groups arranged by the #group_callback function.
     *
     * @return
     *   A render array that will render to a string of JavaScript tags.
     *
     * @see drupal_get_js()
     */
    function drupal_pre_render_scripts($elements) {
      $js_assets = $elements['#items'];
    
      // Aggregate the JavaScript if necessary, but only during normal site
      // operation.
      if (!defined('MAINTENANCE_MODE') && Drupal::config('system.performance')->get('js.preprocess')) {
        $js_assets = \Drupal::service('asset.js.collection_optimizer')->optimize($js_assets);
      }
      return \Drupal::service('asset.js.collection_renderer')->render($js_assets);
    }
    
    /**
     * Adds attachments to a render() structure.
     *
     * Libraries, JavaScript, CSS and other types of custom structures are attached
     * to elements using the #attached property. The #attached property is an
     * associative array, where the keys are the the attachment types and the values
     * are the attached data. For example:
     * @code
     * $build['#attached'] = array(
     *   'library' => array(array('taxonomy', 'taxonomy')),
     *   'css' => array(drupal_get_path('module', 'taxonomy') . '/css/taxonomy.module.css'),
     * );
     * @endcode
     *
     * 'js', 'css', and 'library' are types that get special handling. For any
     * other kind of attached data, the array key must be the full name of the
     * callback function and each value an array of arguments. For example:
     * @code
     * $build['#attached']['drupal_add_http_header'] = array(
     *   array('Content-Type', 'application/rss+xml; charset=utf-8'),
     * );
     * @endcode
     *
     * External 'js' and 'css' files can also be loaded. For example:
     * @code
     * $build['#attached']['js'] = array(
     *   'http://code.jquery.com/jquery-1.4.2.min.js' => array(
     *     'type' => 'external',
     *   ),
     * );
     * @endcode
     *
     * @param $elements
     *   The structured array describing the data being rendered.
     * @param $dependency_check
     *   When TRUE, will exit if a given library's dependencies are missing. When
     *   set to FALSE, will continue to add the libraries, even though one or more
     *   dependencies are missing. Defaults to FALSE.
     *
     * @return
     *   FALSE if there were any missing library dependencies; TRUE if all library
     *   dependencies were met.
     *
     * @see drupal_add_library()
     * @see drupal_add_js()
     * @see drupal_add_css()
     * @see drupal_render()
     */
    function drupal_process_attached($elements, $dependency_check = FALSE) {
      // Add defaults to the special attached structures that should be processed differently.
      $elements['#attached'] += array(
        'library' => array(),
        'js' => array(),
        'css' => array(),
      );
    
      // Add the libraries first.
      $success = TRUE;
      foreach ($elements['#attached']['library'] as $library) {
        if (drupal_add_library($library[0], $library[1]) === FALSE) {
          $success = FALSE;
          // Exit if the dependency is missing.
          if ($dependency_check) {
            return $success;
          }
        }
      }
      unset($elements['#attached']['library']);
    
      // Add both the JavaScript and the CSS.
      // The parameters for drupal_add_js() and drupal_add_css() require special
      // handling.
      foreach (array('js', 'css') as $type) {
        foreach ($elements['#attached'][$type] as $data => $options) {
          // If the value is not an array, it's a filename and passed as first
          // (and only) argument.
          if (!is_array($options)) {
            $data = $options;
            $options = NULL;
          }
          // In some cases, the first parameter ($data) is an array. Arrays can't be
          // passed as keys in PHP, so we have to get $data from the value array.
          if (is_numeric($data)) {
            $data = $options['data'];
            unset($options['data']);
          }
          call_user_func('drupal_add_' . $type, $data, $options);
        }
        unset($elements['#attached'][$type]);
      }
    
      // Add additional types of attachments specified in the render() structure.
      // Libraries, JavaScript and CSS have been added already, as they require
      // special handling.
      foreach ($elements['#attached'] as $callback => $options) {
        foreach ($elements['#attached'][$callback] as $args) {
          call_user_func_array($callback, $args);
        }
      }
    
      return $success;
    }
    
    /**
     * Adds JavaScript to change the state of an element based on another element.
     *
     * A "state" means a certain property on a DOM element, such as "visible" or
     * "checked". A state can be applied to an element, depending on the state of
     * another element on the page. In general, states depend on HTML attributes and
     * DOM element properties, which change due to user interaction.
     *
     * Since states are driven by JavaScript only, it is important to understand
     * that all states are applied on presentation only, none of the states force
     * any server-side logic, and that they will not be applied for site visitors
     * without JavaScript support. All modules implementing states have to make
     * sure that the intended logic also works without JavaScript being enabled.
     *
     * #states is an associative array in the form of:
     * @code
     * array(
     *   STATE1 => CONDITIONS_ARRAY1,
     *   STATE2 => CONDITIONS_ARRAY2,
     *   ...
     * )
     * @endcode
     * Each key is the name of a state to apply to the element, such as 'visible'.
     * Each value is a list of conditions that denote when the state should be
     * applied.
     *
     * Multiple different states may be specified to act on complex conditions:
     * @code
     * array(
     *   'visible' => CONDITIONS,
     *   'checked' => OTHER_CONDITIONS,
     * )
     * @endcode
     *
     * Every condition is a key/value pair, whose key is a jQuery selector that
     * denotes another element on the page, and whose value is an array of
     * conditions, which must bet met on that element:
     * @code
     * array(
     *   'visible' => array(
     *     JQUERY_SELECTOR => REMOTE_CONDITIONS,
     *     JQUERY_SELECTOR => REMOTE_CONDITIONS,
     *     ...
     *   ),
     * )
     * @endcode
     * All conditions must be met for the state to be applied.
     *
     * Each remote condition is a key/value pair specifying conditions on the other
     * element that need to be met to apply the state to the element:
     * @code
     * array(
     *   'visible' => array(
     *     ':input[name="remote_checkbox"]' => array('checked' => TRUE),
     *   ),
     * )
     * @endcode
     *
     * For example, to show a textfield only when a checkbox is checked:
     * @code
     * $form['toggle_me'] = array(
     *   '#type' => 'checkbox',
     *   '#title' => t('Tick this box to type'),
     * );
     * $form['settings'] = array(
     *   '#type' => 'textfield',
     *   '#states' => array(
     *     // Only show this field when the 'toggle_me' checkbox is enabled.
     *     'visible' => array(
     *       ':input[name="toggle_me"]' => array('checked' => TRUE),
     *     ),
     *   ),
     * );
     * @endcode
     *
     * The following states may be applied to an element:
     * - enabled
     * - disabled
     * - required
     * - optional
     * - visible
     * - invisible
     * - checked
     * - unchecked
     * - expanded
     * - collapsed
     *
     * The following states may be used in remote conditions:
     * - empty
     * - filled
     * - checked
     * - unchecked
     * - expanded
     * - collapsed
     * - value
     *
     * The following states exist for both elements and remote conditions, but are
     * not fully implemented and may not change anything on the element:
     * - relevant
     * - irrelevant
     * - valid
     * - invalid
     * - touched
     * - untouched
     * - readwrite
     * - readonly
     *
     * When referencing select lists and radio buttons in remote conditions, a
     * 'value' condition must be used:
     * @code
     *   '#states' => array(
     *     // Show the settings if 'bar' has been selected for 'foo'.
     *     'visible' => array(
     *       ':input[name="foo"]' => array('value' => 'bar'),
     *     ),
     *   ),
     * @endcode
     *
     * @param $elements
     *   A renderable array element having a #states property as described above.
     *
     * @see form_example_states_form()
     */
    function drupal_process_states(&$elements) {
      $elements['#attached']['library'][] = array('system', 'drupal.states');
      $elements['#attached']['js'][] = array(
        'type' => 'setting',
        'data' => array('states' => array('#' . $elements['#id'] => $elements['#states'])),
      );
    }
    
    /**
     * Adds multiple JavaScript or CSS files at the same time.
     *
     * A library defines a set of JavaScript and/or CSS files, optionally using
     * settings, and optionally requiring another library. For example, a library
     * can be a jQuery plugin, a JavaScript framework, or a CSS framework. This
     * function allows modules to load a library defined/shipped by itself or a
     * depending module, without having to add all files of the library separately.
     * Each library is only loaded once.
     *
     * @param $module
     *   The name of the module that registered the library.
     * @param $name
     *   The name of the library to add.
     * @param $every_page
     *   Set to TRUE if this library is added to every page on the site.
     *
     * @return
     *   TRUE if the library was successfully added; FALSE if the library or one of
     *   its dependencies could not be added.
     *
     * @see drupal_get_library()
     * @see hook_library_info()
     * @see hook_library_info_alter()
     */
    function drupal_add_library($module, $name, $every_page = NULL) {
      $added = &drupal_static(__FUNCTION__, array());
    
      // Only process the library if it exists and it was not added already.
      if (!isset($added[$module][$name])) {
        if ($library = drupal_get_library($module, $name)) {
          // Add all components within the library.
          $elements['#attached'] = array(
            'library' => $library['dependencies'],
            'js' => $library['js'],
            'css' => $library['css'],
          );
          foreach (array('js', 'css') as $type) {
            foreach ($elements['#attached'][$type] as $data => $options) {
              // Apply the JS_LIBRARY group if it isn't explicitly given.
              if ($type == 'js' && !isset($options['group'])) {
                $elements['#attached']['js'][$data]['group'] = JS_LIBRARY;
              }
              // Set the every_page flag if one was passed.
              if (isset($every_page)) {
                $elements['#attached'][$type][$data]['every_page'] = $every_page;
              }
            }
          }
    
          $added[$module][$name] = drupal_process_attached($elements, TRUE);
        }
        else {
          // Requested library does not exist.
          $added[$module][$name] = FALSE;
        }
      }
    
      return $added[$module][$name];
    }
    
    /**
     * Retrieves information for a JavaScript/CSS library.
     *
     * Library information is statically cached. Libraries are keyed by module for
     * several reasons:
     * - Libraries are not unique. Multiple modules might ship with the same library
     *   in a different version or variant. This registry cannot (and does not
     *   attempt to) prevent library conflicts.
     * - Modules implementing and thereby depending on a library that is registered
     *   by another module can only rely on that module's library.
     * - Two (or more) modules can still register the same library and use it
     *   without conflicts in case the libraries are loaded on certain pages only.
     *
     * @param $module
     *   The name of a module that registered a library.
     * @param $name
     *   (optional) The name of a registered library to retrieve. By default, all
     *   libraries registered by $module are returned.
     *
     * @return
     *   The definition of the requested library, if $name was passed and it exists,
     *   or FALSE if it does not exist. If no $name was passed, an associative array
     *   of libraries registered by $module is returned (which may be empty).
     *
     * @see drupal_add_library()
     * @see hook_library_info()
     * @see hook_library_info_alter()
     *
     * @todo The purpose of drupal_get_*() is completely different to other page
     *   requisite API functions; find and use a different name.
     */
    function drupal_get_library($module, $name = NULL) {
      $libraries = &drupal_static(__FUNCTION__, array());
    
      if (!isset($libraries[$module])) {
        // Retrieve all libraries associated with the module.
        $module_libraries = module_invoke($module, 'library_info');
        if (empty($module_libraries)) {
          $module_libraries = array();
        }
        // Allow modules to alter the module's registered libraries.
        drupal_alter('library_info', $module_libraries, $module);
    
        foreach ($module_libraries as $key => $data) {
          if (is_array($data)) {
            // Add default elements to allow for easier processing.
            $module_libraries[$key] += array('dependencies' => array(), 'js' => array(), 'css' => array());
            foreach ($module_libraries[$key]['js'] as $file => $options) {
              if (is_scalar($options)) {
                // The JavaScript or CSS file has been specified in shorthand
                // format, without an array of options. In this case $options is the
                // filename. Convert the shorthand version and remove the old array
                // key.
                unset($module_libraries[$key]['js'][$file]);
                $file = $options;
                $options = array();
              }
              $module_libraries[$key]['js'][$file]['version'] = $module_libraries[$key]['version'];
            }
          }
        }
        $libraries[$module] = $module_libraries;
      }
      if (isset($name)) {
        if (!isset($libraries[$module][$name])) {
          $libraries[$module][$name] = FALSE;
        }
        return $libraries[$module][$name];
      }
      return $libraries[$module];
    }
    
    /**
     * Assists in adding the tableDrag JavaScript behavior to a themed table.
     *
     * Draggable tables should be used wherever an outline or list of sortable items
     * needs to be arranged by an end-user. Draggable tables are very flexible and
     * can manipulate the value of form elements placed within individual columns.
     *
     * To set up a table to use drag and drop in place of weight select-lists or in
     * place of a form that contains parent relationships, the form must be themed
     * into a table. The table must have an ID attribute set. If using
     * theme_table(), the ID may be set as follows:
     * @code
     * $output = theme('table', array('header' => $header, 'rows' => $rows, 'attributes' => array('id' => 'my-module-table')));
     * return $output;
     * @endcode
     *
     * In the theme function for the form, a special class must be added to each
     * form element within the same column, "grouping" them together.
     *
     * In a situation where a single weight column is being sorted in the table, the
     * classes could be added like this (in the theme function):
     * @code
     * $form['my_elements'][$delta]['weight']['#attributes']['class'] = array('my-elements-weight');
     * @endcode
     *
     * Each row of the table must also have a class of "draggable" in order to
     * enable the drag handles:
     * @code
     * $row = array(...);
     * $rows[] = array(
     *   'data' => $row,
     *   'class' => array('draggable'),
     * );
     * @endcode
     *
     * When tree relationships are present, the two additional classes
     * 'tabledrag-leaf' and 'tabledrag-root' can be used to refine the behavior:
     * - Rows with the 'tabledrag-leaf' class cannot have child rows.
     * - Rows with the 'tabledrag-root' class cannot be nested under a parent row.
     *
     * Calling drupal_add_tabledrag() would then be written as such:
     * @code
     * drupal_add_tabledrag('my-module-table', 'order', 'sibling', 'my-elements-weight');
     * @endcode
     *
     * In a more complex case where there are several groups in one column (such as
     * the block regions on the admin/structure/block page), a separate subgroup
     * class must also be added to differentiate the groups.
     * @code
     * $form['my_elements'][$region][$delta]['weight']['#attributes']['class'] = array('my-elements-weight', 'my-elements-weight-' . $region);
     * @endcode
     *
     * $group is still 'my-element-weight', and the additional $subgroup variable
     * will be passed in as 'my-elements-weight-' . $region. This also means that
     * you'll need to call drupal_add_tabledrag() once for every region added.
     *
     * @code
     * foreach ($regions as $region) {
     *   drupal_add_tabledrag('my-module-table', 'order', 'sibling', 'my-elements-weight', 'my-elements-weight-' . $region);
     * }
     * @endcode
     *
     * In a situation where tree relationships are present, adding multiple
     * subgroups is not necessary, because the table will contain indentations that
     * provide enough information about the sibling and parent relationships. See
     * theme_menu_overview_form() for an example creating a table containing parent
     * relationships.
     *
     * Note that this function should be called from the theme layer, such as in a
     * .tpl.php file, theme_ function, or in a template_preprocess function, not in
     * a form declaration. Though the same JavaScript could be added to the page
     * using drupal_add_js() directly, this function helps keep template files
     * clean and readable. It also prevents tabledrag.js from being added twice
     * accidentally.
     *
     * @param $table_id
     *   String containing the target table's id attribute. If the table does not
     *   have an id, one will need to be set, such as <table id="my-module-table">.
     * @param $action
     *   String describing the action to be done on the form item. Either 'match'
     *   'depth', or 'order'. Match is typically used for parent relationships.
     *   Order is typically used to set weights on other form elements with the same
     *   group. Depth updates the target element with the current indentation.
     * @param $relationship
     *   String describing where the $action variable should be performed. Either
     *   'parent', 'sibling', 'group', or 'self'. Parent will only look for fields
     *   up the tree. Sibling will look for fields in the same group in rows above
     *   and below it. Self affects the dragged row itself. Group affects the
     *   dragged row, plus any children below it (the entire dragged group).
     * @param $group
     *   A class name applied on all related form elements for this action.
     * @param $subgroup
     *   (optional) If the group has several subgroups within it, this string should
     *   contain the class name identifying fields in the same subgroup.
     * @param $source
     *   (optional) If the $action is 'match', this string should contain the class
     *   name identifying what field will be used as the source value when matching
     *   the value in $subgroup.
     * @param $hidden
     *   (optional) The column containing the field elements may be entirely hidden
     *   from view dynamically when the JavaScript is loaded. Set to FALSE if the
     *   column should not be hidden.
     * @param $limit
     *   (optional) Limit the maximum amount of parenting in this table.
     * @see block-admin-display-form.tpl.php
     * @see theme_menu_overview_form()
     */
    function drupal_add_tabledrag($table_id, $action, $relationship, $group, $subgroup = NULL, $source = NULL, $hidden = TRUE, $limit = 0) {
      $js_added = &drupal_static(__FUNCTION__, FALSE);
      $tabledrag_id = &drupal_static(__FUNCTION__  . '_setting', FALSE);
      $tabledrag_id = (!isset($tabledrag_id)) ? 0 : $tabledrag_id + 1;
    
      if (!$js_added) {
        // Add the table drag JavaScript to the page before the module JavaScript
        // to ensure that table drag behaviors are registered before any module
        // uses it.
        drupal_add_library('system', 'drupal.tabledrag');
        $js_added = TRUE;
      }
    
      // If a subgroup or source isn't set, assume it is the same as the group.
      $target = isset($subgroup) ? $subgroup : $group;
      $source = isset($source) ? $source : $target;
      $settings['tableDrag'][$table_id][$group][$tabledrag_id] = array(
        'target' => $target,
        'source' => $source,
        'relationship' => $relationship,
        'action' => $action,
        'hidden' => $hidden,
        'limit' => $limit,
      );
      drupal_add_js($settings, 'setting');
    }
    
    /**
     * Deletes old cached JavaScript files and variables.
     */
    function drupal_clear_js_cache() {
      Drupal::state()->delete('system.javascript_parsed');
      Drupal::state()->delete('system.js_cache_files');
      file_scan_directory('public://js', '/.*/', array('callback' => 'drupal_delete_file_if_stale'));
    }
    
    /**
     * Converts a PHP variable into its JavaScript equivalent.
     *
     * We use HTML-safe strings, with several characters escaped.
     *
     * @see drupal_json_decode()
     * @ingroup php_wrappers
     * @deprecated as of Drupal 8.0. Use Drupal\Component\Utility\Json::encode()
     *   directly instead.
     */
    function drupal_json_encode($var) {
      return Json::encode($var);
    }
    
    /**
     * Converts an HTML-safe JSON string into its PHP equivalent.
     *
     * @see drupal_json_encode()
     * @ingroup php_wrappers
     * @deprecated as of Drupal 8.0. Use Drupal\Component\Utility\Json::decode()
     *   directly instead.
     */
    function drupal_json_decode($var) {
      return Json::decode($var);
    }
    
    /**
     * Ensures the private key variable used to generate tokens is set.
     *
     * @return string
     *   The private key.
     *
     * @see \Drupal\Core\Access\CsrfTokenManager
     *
     * @deprecated as of Drupal 8.0. Use the 'private_key' service instead.
     */
    function drupal_get_private_key() {
      return \Drupal::service('private_key')->get();
    }
    
    /**
     * Generates a token based on $value, the user session, and the private key.
     *
     * @param string $value
     *   An additional value to base the token on.
     *
     * @return string
     *   A 43-character URL-safe token for validation, based on the user session ID,
     *   the hash salt provided from drupal_get_hash_salt(), and the
     *   'drupal_private_key' configuration variable.
     *
     * @see drupal_get_hash_salt()
     * @see \Drupal\Core\Access\CsrfTokenManager
     *
     * @deprecated as of Drupal 8.0. Use the csrf_token service instead.
     */
    function drupal_get_token($value = '') {
      return \Drupal::csrfToken()->get($value);
    }
    
    /**
     * Validates a token based on $value, the user session, and the private key.
     *
     * @param string $token
     *   The token to be validated.
     * @param string $value
     *   An additional value to base the token on.
     * @param bool $skip_anonymous
     *   Set to true to skip token validation for anonymous users.
     *
     * @return bool
     *   True for a valid token, false for an invalid token. When $skip_anonymous
     *   is true, the return value will always be true for anonymous users.
     *
     * @see \Drupal\Core\Access\CsrfTokenManager
     *
     * @deprecated as of Drupal 8.0. Use the csrf_token service instead.
     */
    function drupal_valid_token($token, $value = '', $skip_anonymous = FALSE) {
      return \Drupal::csrfToken()->validate($token, $value, $skip_anonymous);
    }
    
    /**
     * Loads code for subsystems and modules, and registers stream wrappers.
     */
    function _drupal_bootstrap_code() {
      require_once __DIR__ . '/../../' . settings()->get('path_inc', 'core/includes/path.inc');
      require_once __DIR__ . '/module.inc';
      require_once __DIR__ . '/theme.inc';
      require_once __DIR__ . '/pager.inc';
      require_once __DIR__ . '/../../' . settings()->get('menu_inc', 'core/includes/menu.inc');
      require_once __DIR__ . '/tablesort.inc';
      require_once __DIR__ . '/file.inc';
      require_once __DIR__ . '/unicode.inc';
      require_once __DIR__ . '/form.inc';
      require_once __DIR__ . '/mail.inc';
      require_once __DIR__ . '/ajax.inc';
      require_once __DIR__ . '/errors.inc';
      require_once __DIR__ . '/schema.inc';
      require_once __DIR__ . '/entity.inc';
    
      // Load all enabled modules
      Drupal::moduleHandler()->loadAll();
    
      // Make sure all stream wrappers are registered.
      file_get_stream_wrappers();
    
      // Now that stream wrappers are registered, log fatal errors from a simpletest
      // child site to a test specific file directory.
      $test_info = &$GLOBALS['drupal_test_info'];
      if (!empty($test_info['in_child_site'])) {
        ini_set('log_errors', 1);
        ini_set('error_log', 'public://error.log');
      }
    
      // Set the allowed protocols once we have the config available.
      $allowed_protocols = Drupal::config('system.filter')->get('protocols');
      if (!isset($allowed_protocols)) {
        // filter_xss_admin() is called by the installer and update.php, in which
        // case the configuration may not exist (yet). Provide a minimal default set
        // of allowed protocols for these cases.
        $allowed_protocols = array('http', 'https');
      }
      Url::setAllowedProtocols($allowed_protocols);
    }
    
    /**
     * Temporary BC function for scripts not using DrupalKernel.
     *
     * DrupalKernel skips this and replicates it via event listeners.
     *
     * @see Drupal\Core\EventSubscriber\PathSubscriber;
     * @see Drupal\Core\EventSubscriber\LegacyRequestSubscriber;
     */
    function _drupal_bootstrap_full($skip = FALSE) {
      static $called = FALSE;
    
      if ($called || $skip) {
        $called = TRUE;
        return;
      }
    
      // Initialize language (which can strip path prefix) prior to initializing
      // current_path().
      drupal_language_initialize();
    
      // Let all modules take action before the menu system handles the request.
      // We do not want this while running update.php.
      if (!defined('MAINTENANCE_MODE') || MAINTENANCE_MODE != 'update') {
        menu_set_custom_theme();
        drupal_theme_initialize();
      }
    }
    
    /**
     * Stores the current page in the cache.
     *
     * If page_compression is enabled, a gzipped version of the page is stored in
     * the cache to avoid compressing the output on each request. The cache entry
     * is unzipped in the relatively rare event that the page is requested by a
     * client without gzip support.
     *
     * Page compression requires the PHP zlib extension
     * (http://php.net/manual/ref.zlib.php).
     *
     * @param $body
     *   The response body.
     * @return
     *   The cached object or NULL if the page cache was not set.
     *
     * @see drupal_page_header()
     */
    function drupal_page_set_cache(Response $response, Request $request) {
      if (drupal_page_is_cacheable()) {
    
        // Check if the current page may be compressed.
        $page_compressed = Drupal::config('system.performance')->get('response.gzip') && extension_loaded('zlib');
    
        $cache = (object) array(
          'cid' => drupal_page_cache_get_cid($request),
          'data' => array(
            'path' => $request->attributes->get('_system_path'),
            'body' => $response->getContent(),
            'title' => drupal_get_title(),
            'headers' => array(),
            // We need to store whether page was compressed or not,
            // because by the time it is read, the configuration might change.
            'page_compressed' => $page_compressed,
          ),
          'tags' => array('content' => TRUE),
          'expire' => CacheBackendInterface::CACHE_PERMANENT,
          'created' => REQUEST_TIME,
        );
    
        $cache->data['headers'] = $response->headers->all();
    
        // Hack: exclude the x-drupal-cache header; it may make it in here because
        // of awkwardness in how we defer sending it over in _drupal_page_get_cache.
        if (isset($cache->data['headers']['x-drupal-cache'])) {
          unset($cache->data['headers']['x-drupal-cache']);
        }
    
         // Use the actual timestamp from an Expires header, if available.
        if ($date = $response->getExpires()) {
          $date = DrupalDateTime::createFromDateTime($date);
          $cache->expire = $date->getTimestamp();
        }
    
        if ($cache->data['body']) {
          if ($page_compressed) {
            $cache->data['body'] = gzencode($cache->data['body'], 9, FORCE_GZIP);
          }
          cache('page')->set($cache->cid, $cache->data, $cache->expire, $cache->tags);
        }
        return $cache;
      }
    }
    
    /**
     * Executes a cron run when called.
     *
     * Do not call this function from a test. Use $this->cronRun() instead.
     *
     * @return
     *   TRUE if cron ran successfully.
     */
    function drupal_cron_run() {
      // Allow execution to continue even if the request gets canceled.
      @ignore_user_abort(TRUE);
    
      // Prevent session information from being saved while cron is running.
      $original_session_saving = drupal_save_session();
      drupal_save_session(FALSE);
    
      // Force the current user to anonymous to ensure consistent permissions on
      // cron runs.
      $original_user = $GLOBALS['user'];
      $GLOBALS['user'] = drupal_anonymous_user();
    
      // Try to allocate enough time to run all the hook_cron implementations.
      drupal_set_time_limit(240);
    
      $return = FALSE;
      // Grab the defined cron queues.
      $queues = Drupal::moduleHandler()->invokeAll('queue_info');
      drupal_alter('queue_info', $queues);
    
      // Try to acquire cron lock.
      if (!lock()->acquire('cron', 240.0)) {
        // Cron is still running normally.
        watchdog('cron', 'Attempting to re-run cron while it is already running.', array(), WATCHDOG_WARNING);
      }
      else {
        // Make sure every queue exists. There is no harm in trying to recreate an
        // existing queue.
        foreach ($queues as $queue_name => $info) {
          if (isset($info['cron'])) {
            Drupal::queue($queue_name)->createQueue();
          }
        }
    
        // Iterate through the modules calling their cron handlers (if any):
        foreach (Drupal::moduleHandler()->getImplementations('cron') as $module) {
          // Do not let an exception thrown by one module disturb another.
          try {
            module_invoke($module, 'cron');
          }
          catch (Exception $e) {
            watchdog_exception('cron', $e);
          }
        }
    
        // Record cron time.
        Drupal::state()->set('system.cron_last', REQUEST_TIME);
        watchdog('cron', 'Cron run completed.', array(), WATCHDOG_NOTICE);
    
        // Release cron lock.
        lock()->release('cron');
    
        // Return TRUE so other functions can check if it did run successfully
        $return = TRUE;
      }
    
      foreach ($queues as $queue_name => $info) {
        if (isset($info['cron'])) {
          $callback = $info['worker callback'];
          $end = time() + (isset($info['cron']['time']) ? $info['cron']['time'] : 15);
          $queue = Drupal::queue($queue_name);
          while (time() < $end && ($item = $queue->claimItem())) {
            call_user_func_array($callback, array($item->data));
            $queue->deleteItem($item);
          }
        }
      }
      // Restore the user.
      $GLOBALS['user'] = $original_user;
      drupal_save_session($original_session_saving);
    
      return $return;
    }
    
    /**
     * This function is kept only for backward compatibility.
     *
     * @see \Drupal\Core\SystemListing::scan().
     */
    function drupal_system_listing($mask, $directory, $key = 'name', $min_depth = 1) {
      // As SystemListing is required to build a dependency injection container
      // from scratch and SystemListingInfo only extends SystemLising, this
      // class needs to be hardwired.
      $listing = new SystemListingInfo();
      return $listing->scan($mask, $directory, $key, $min_depth);
    }
    
    /**
     * Sets the main page content value for later use.
     *
     * Given the nature of the Drupal page handling, this will be called once with
     * a string or array. We store that and return it later as the block is being
     * displayed.
     *
     * @param $content
     *   A string or renderable array representing the body of the page.
     *
     * @return
     *   If called without $content, a renderable array representing the body of
     *   the page.
     */
    function drupal_set_page_content($content = NULL) {
      $content_block = &drupal_static(__FUNCTION__, NULL);
      $main_content_display = &drupal_static('system_main_content_added', FALSE);
    
      // Filter out each empty value, though allow '0' and 0, which would be
      // filtered out by empty().
      if ($content !== NULL && $content !== '') {
        $content_block = (is_array($content) ? $content : array('main' => array('#markup' => $content)));
      }
      else {
        // Indicate that the main content has been requested. We assume that
        // the module requesting the content will be adding it to the page.
        // A module can indicate that it does not handle the content by setting
        // the static variable back to FALSE after calling this function.
        $main_content_display = TRUE;
        return $content_block;
      }
    }
    
    /**
     * Pre-render callback: Renders #browsers into #prefix and #suffix.
     *
     * @param $elements
     *   A render array with a '#browsers' property. The '#browsers' property can
     *   contain any or all of the following keys:
     *   - 'IE': If FALSE, the element is not rendered by Internet Explorer. If
     *     TRUE, the element is rendered by Internet Explorer. Can also be a string
     *     containing an expression for Internet Explorer to evaluate as part of a
     *     conditional comment. For example, this can be set to 'lt IE 7' for the
     *     element to be rendered in Internet Explorer 6, but not in Internet
     *     Explorer 7 or higher. Defaults to TRUE.
     *   - '!IE': If FALSE, the element is not rendered by browsers other than
     *     Internet Explorer. If TRUE, the element is rendered by those browsers.
     *     Defaults to TRUE.
     *   Examples:
     *   - To render an element in all browsers, '#browsers' can be left out or set
     *     to array('IE' => TRUE, '!IE' => TRUE).
     *   - To render an element in Internet Explorer only, '#browsers' can be set
     *     to array('!IE' => FALSE).
     *   - To render an element in Internet Explorer 6 only, '#browsers' can be set
     *     to array('IE' => 'lt IE 7', '!IE' => FALSE).
     *   - To render an element in Internet Explorer 8 and higher and in all other
     *     browsers, '#browsers' can be set to array('IE' => 'gte IE 8').
     *
     * @return
     *   The passed-in element with markup for conditional comments potentially
     *   added to '#prefix' and '#suffix'.
     */
    function drupal_pre_render_conditional_comments($elements) {
      $browsers = isset($elements['#browsers']) ? $elements['#browsers'] : array();
      $browsers += array(
        'IE' => TRUE,
        '!IE' => TRUE,
      );
    
      // If rendering in all browsers, no need for conditional comments.
      if ($browsers['IE'] === TRUE && $browsers['!IE']) {
        return $elements;
      }
    
      // Determine the conditional comment expression for Internet Explorer to
      // evaluate.
      if ($browsers['IE'] === TRUE) {
        $expression = 'IE';
      }
      elseif ($browsers['IE'] === FALSE) {
        $expression = '!IE';
      }
      else {
        $expression = $browsers['IE'];
      }
    
      // Wrap the element's potentially existing #prefix and #suffix properties with
      // conditional comment markup. The conditional comment expression is evaluated
      // by Internet Explorer only. To control the rendering by other browsers,
      // either the "downlevel-hidden" or "downlevel-revealed" technique must be
      // used. See http://en.wikipedia.org/wiki/Conditional_comment for details.
      $elements += array(
        '#prefix' => '',
        '#suffix' => '',
      );
      if (!$browsers['!IE']) {
        // "downlevel-hidden".
        $elements['#prefix'] = "\n<!--[if $expression]>\n" . $elements['#prefix'];
        $elements['#suffix'] .= "<![endif]-->\n";
      }
      else {
        // "downlevel-revealed".
        $elements['#prefix'] = "\n<!--[if $expression]><!-->\n" . $elements['#prefix'];
        $elements['#suffix'] .= "<!--<![endif]-->\n";
      }
    
      return $elements;
    }
    
    /**
     * Pre-render callback: Renders a generic HTML tag with attributes into #markup.
     *
     * @param array $element
     *   An associative array containing:
     *   - #tag: The tag name to output. Typical tags added to the HTML HEAD:
     *     - meta: To provide meta information, such as a page refresh.
     *     - link: To refer to stylesheets and other contextual information.
     *     - script: To load JavaScript.
     *   - #attributes: (optional) An array of HTML attributes to apply to the
     *     tag.
     *   - #value: (optional) A string containing tag content, such as inline
     *     CSS.
     *   - #value_prefix: (optional) A string to prepend to #value, e.g. a CDATA
     *     wrapper prefix.
     *   - #value_suffix: (optional) A string to append to #value, e.g. a CDATA
     *     wrapper suffix.
     */
    function drupal_pre_render_html_tag($element) {
      $attributes = isset($element['#attributes']) ? new Attribute($element['#attributes']) : '';
      if (!isset($element['#value'])) {
        $markup = '<' . $element['#tag'] . $attributes . " />\n";
      }
      else {
        $markup = '<' . $element['#tag'] . $attributes . '>';
        if (isset($element['#value_prefix'])) {
          $markup .= $element['#value_prefix'];
        }
        $markup .= $element['#value'];
        if (isset($element['#value_suffix'])) {
          $markup .= $element['#value_suffix'];
        }
        $markup .= '</' . $element['#tag'] . ">\n";
      }
      $element['#markup'] = $markup;
      return $element;
    }
    
    /**
     * Pre-render callback: Renders a link into #markup.
     *
     * Doing so during pre_render gives modules a chance to alter the link parts.
     *
     * @param $elements
     *   A structured array whose keys form the arguments to l():
     *   - #title: The link text to pass as argument to l().
     *   - One of the following
     *     - #route_name and (optionally) and a #route_parameters array; The route
     *       name and route parameters which will be passed into the link generator.
     *     - #href: The system path or URL to pass as argument to l().
     *   - #options: (optional) An array of options to pass to l() or the link
     *     generator.
     *
     * @return
     *   The passed-in elements containing a rendered link in '#markup'.
     */
    function drupal_pre_render_link($element) {
      // By default, link options to pass to l() are normally set in #options.
      $element += array('#options' => array());
      // However, within the scope of renderable elements, #attributes is a valid
      // way to specify attributes, too. Take them into account, but do not override
      // attributes from #options.
      if (isset($element['#attributes'])) {
        $element['#options'] += array('attributes' => array());
        $element['#options']['attributes'] += $element['#attributes'];
      }
    
      // This #pre_render callback can be invoked from inside or outside of a Form
      // API context, and depending on that, a HTML ID may be already set in
      // different locations. #options should have precedence over Form API's #id.
      // #attributes have been taken over into #options above already.
      if (isset($element['#options']['attributes']['id'])) {
        $element['#id'] = $element['#options']['attributes']['id'];
      }
      elseif (isset($element['#id'])) {
        $element['#options']['attributes']['id'] = $element['#id'];
      }
    
      // Conditionally invoke ajax_pre_render_element(), if #ajax is set.
      if (isset($element['#ajax']) && !isset($element['#ajax_processed'])) {
        // If no HTML ID was found above, automatically create one.
        if (!isset($element['#id'])) {
          $element['#id'] = $element['#options']['attributes']['id'] = drupal_html_id('ajax-link');
        }
        // If #ajax['path] was not specified, use the href as Ajax request URL.
        if (!isset($element['#ajax']['path'])) {
          $element['#ajax']['path'] = $element['#href'];
          $element['#ajax']['options'] = $element['#options'];
        }
        $element = ajax_pre_render_element($element);
      }
    
      if (isset($element['#route_name'])) {
        $element['#route_parameters'] = empty($element['#route_parameters']) ? array() : $element['#route_parameters'];
        $element['#markup'] = Drupal::linkGenerator()->generate($element['#title'], $element['#route_name'], $element['#route_parameters'], $element['#options']);
      }
      else {
        $element['#markup'] = l($element['#title'], $element['#href'], $element['#options']);
      }
      return $element;
    }
    
    /**
     * Pre-render callback: Collects child links into a single array.
     *
     * This function can be added as a pre_render callback for a renderable array,
     * usually one which will be themed by theme_links(). It iterates through all
     * unrendered children of the element, collects any #links properties it finds,
     * merges them into the parent element's #links array, and prevents those
     * children from being rendered separately.
     *
     * The purpose of this is to allow links to be logically grouped into related
     * categories, so that each child group can be rendered as its own list of
     * links if drupal_render() is called on it, but calling drupal_render() on the
     * parent element will still produce a single list containing all the remaining
     * links, regardless of what group they were in.
     *
     * A typical example comes from node links, which are stored in a renderable
     * array similar to this:
     * @code
     * $node->content['links'] = array(
     *   '#theme' => 'links__node',
     *   '#pre_render' => array('drupal_pre_render_links'),
     *   'comment' => array(
     *     '#theme' => 'links__node__comment',
     *     '#links' => array(
     *       // An array of links associated with node comments, suitable for
     *       // passing in to theme_links().
     *     ),
     *   ),
     *   'statistics' => array(
     *     '#theme' => 'links__node__statistics',
     *     '#links' => array(
     *       // An array of links associated with node statistics, suitable for
     *       // passing in to theme_links().
     *     ),
     *   ),
     *   'translation' => array(
     *     '#theme' => 'links__node__translation',
     *     '#links' => array(
     *       // An array of links associated with node translation, suitable for
     *       // passing in to theme_links().
     *     ),
     *   ),
     * );
     * @endcode
     *
     * In this example, the links are grouped by functionality, which can be
     * helpful to themers who want to display certain kinds of links independently.
     * For example, adding this code to node.html.twig will result in the comment
     * links being rendered as a single list:
     * @code
     * {{ content.links.comment }}
     * @endcode
     *
     * (where $node->content has been transformed into $content before handing
     * control to the node.html.twig template).
     *
     * The pre_render function defined here allows the above flexibility, but also
     * allows the following code to be used to render all remaining links into a
     * single list, regardless of their group:
     * @code
     * {{ content.links }}
     * @endcode
     *
     * In the above example, this will result in the statistics and translation
     * links being rendered together in a single list (but not the comment links,
     * which were rendered previously on their own).
     *
     * Because of the way this function works, the individual properties of each
     * group (for example, a group-specific #theme property such as
     * 'links__node__comment' in the example above, or any other property such as
     * #attributes or #pre_render that is attached to it) are only used when that
     * group is rendered on its own. When the group is rendered together with other
     * children, these child-specific properties are ignored, and only the overall
     * properties of the parent are used.
     */
    function drupal_pre_render_links($element) {
      $element += array('#links' => array());
      foreach (element_children($element) as $key) {
        $child = &$element[$key];
        // If the child has links which have not been printed yet and the user has
        // access to it, merge its links in to the parent.
        if (isset($child['#links']) && empty($child['#printed']) && (!isset($child['#access']) || $child['#access'])) {
          $element['#links'] += $child['#links'];
          // Mark the child as having been printed already (so that its links
          // cannot be mistakenly rendered twice).
          $child['#printed'] = TRUE;
        }
      }
      return $element;
    }
    
    /**
     * Pre-render callback: Attaches the dropbutton library and required markup.
     */
    function drupal_pre_render_dropbutton($element) {
      $element['#attached']['library'][] = array('system', 'drupal.dropbutton');
      $element['#attributes']['class'][] = 'dropbutton';
      if (!isset($element['#theme_wrappers'])) {
        $element['#theme_wrappers'] = array();
      }
      array_unshift($element['#theme_wrappers'], 'dropbutton_wrapper');
    
      // Enable targeted theming of specific dropbuttons (e.g., 'operations' or
      // 'operations__node').
      if (isset($element['#subtype'])) {
        $element['#theme'] .= '__' . $element['#subtype'];
      }
    
      return $element;
    }
    
    /**
     * Renders the page, including all theming.
     *
     * @param $page
     *   A string or array representing the content of a page. The array consists of
     *   the following keys:
     *   - #type: Value is always 'page'. This pushes the theming through
     *     the page template (required).
     *   - #show_messages: Suppress drupal_get_message() items. Used by Batch
     *     API (optional).
     *
     * @see hook_page_alter()
     * @see element_info()
     */
    function drupal_render_page($page) {
      $main_content_display = &drupal_static('system_main_content_added', FALSE);
    
      // Pull out the page title to set it back later.
      if (is_array($page) && isset($page['#title'])) {
        $title = $page['#title'];
      }
    
      // Allow menu callbacks to return strings or arbitrary arrays to render.
      // If the array returned is not of #type page directly, we need to fill
      // in the page with defaults.
      if (is_string($page) || (is_array($page) && (!isset($page['#type']) || ($page['#type'] != 'page')))) {
        drupal_set_page_content($page);
        $page = element_info('page');
      }
    
      // Modules can add elements to $page as needed in hook_page_build().
      foreach (Drupal::moduleHandler()->getImplementations('page_build') as $module) {
        $function = $module . '_page_build';
        $function($page);
      }
      // Modules alter the $page as needed. Blocks are populated into regions like
      // 'sidebar_first', 'footer', etc.
      drupal_alter('page', $page);
    
      // If no module has taken care of the main content, add it to the page now.
      // This allows the site to still be usable even if no modules that
      // control page regions (for example, the Block module) are enabled.
      if (!$main_content_display) {
        $page['content']['system_main'] = drupal_set_page_content();
      }
    
      // Set back the previously stored title.
      if (isset($title)) {
        $page['#title'] = $title;
      }
    
      return drupal_render($page);
    }
    
    /**
     * Renders HTML given a structured array tree.
     *
     * Renderable arrays have two kinds of key/value pairs: properties and children.
     * Properties have keys starting with '#' and their values influence how the
     * array will be rendered. Children are all elements whose keys do not start
     * with a '#'. Their values should be renderable arrays themselves, which will
     * be rendered during the rendering of the parent array. The markup provided by
     * the children is typically inserted into the markup generated by the parent
     * array.
     *
     * The process of rendering an element is recursive unless the element defines
     * an implemented theme hook in #theme. During each call to drupal_render(), the
     * outermost renderable array (also known as an "element") is processed using
     * the following steps:
     *   - If this element has already been printed (#printed = TRUE) or the user
     *     does not have access to it (#access = FALSE), then an empty string is
     *     returned.
     *   - If this element has #cache defined then the cached markup for this
     *     element will be returned if it exists in drupal_render()'s cache. To use
     *     drupal_render() caching, set the element's #cache property to an
     *     associative array with one or several of the following keys:
     *     - 'keys': An array of one or more keys that identify the element. If
     *       'keys' is set, the cache ID is created automatically from these keys.
     *       See drupal_render_cid_create().
     *     - 'granularity' (optional): Define the cache granularity using binary
     *       combinations of the cache granularity constants, e.g.
     *       DRUPAL_CACHE_PER_USER to cache for each user separately or
     *       DRUPAL_CACHE_PER_PAGE | DRUPAL_CACHE_PER_ROLE to cache separately for
     *       each page and role. If not specified the element is cached globally for
     *       each theme and language.
     *     - 'cid': Specify the cache ID directly. Either 'keys' or 'cid' is
     *       required. If 'cid' is set, 'keys' and 'granularity' are ignored. Use
     *       only if you have special requirements.
     *     - 'expire': Set to one of the cache lifetime constants.
     *     - 'bin': Specify a cache bin to cache the element in. Default is 'cache'.
     *   - If this element has #type defined and the default attributes for this
     *     element have not already been merged in (#defaults_loaded = TRUE) then
     *     the defaults for this type of element, defined in hook_element_info(),
     *     are merged into the array. #defaults_loaded is set by functions that
     *     process render arrays and call element_info() before passing the array to
     *     drupal_render(), such as form_builder() in the Form API.
     *   - If this element has an array of #pre_render functions defined, they are
     *     called sequentially to modify the element before rendering. After all the
     *     #pre_render functions have been called, #printed is checked a second time
     *     in case a #pre_render function flags the element as printed.
     *   - The child elements of this element are sorted by weight using uasort() in
     *     element_children(). Since this is expensive, when passing already sorted
     *     elements to drupal_render(), for example from a database query, set
     *     $elements['#sorted'] = TRUE to avoid sorting them a second time.
     *   - The main render phase to produce #children for this element takes place:
     *     - If this element has #theme defined and #theme is an implemented theme
     *       hook/suggestion then theme() is called and must render both the element
     *       and its children. If #render_children is set, theme() will not be
     *       called. #render_children is usually only set internally by theme() so
     *       that we can avoid the situation where drupal_render() called from
     *       within a theme preprocess function creates an infinite loop.
     *     - If this element does not have a defined #theme, or the defined #theme
     *       hook is not implemented, or #render_children is set, then
     *       drupal_render() is called recursively on each of the child elements of
     *       this element, and the result of each is concatenated onto #children.
     *       This is skipped if #children is not empty at this point.
     *     - Once #children has been rendered for this element, if #theme is not
     *       implemented and #markup is set for this element, #markup will be
     *       prepended to #children.
     *   - If this element has #states defined then JavaScript state information is
     *     added to this element's #attached attribute by drupal_process_states().
     *   - If this element has #attached defined then any required libraries,
     *     JavaScript, CSS, or other custom data are added to the current page by
     *     drupal_process_attached().
     *   - If this element has an array of #theme_wrappers defined and
     *     #render_children is not set, #children is then re-rendered by passing the
     *     element in its current state to theme() successively for each item in
     *     #theme_wrappers. Since #theme and #theme_wrappers hooks often define
     *     variables with the same names it is possible to explicitly override each
     *     attribute passed to each #theme_wrappers hook by setting the hook name as
     *     the key and an array of overrides as the value in #theme_wrappers array.
     *     For example, if we have a render element as follows:
     *     @code
     *     array(
     *       '#theme' => 'image',
     *       '#attributes' => array('class' => 'foo'),
     *       '#theme_wrappers' => array('container'),
     *     );
     *     @endcode
     *     and we need to pass the class 'bar' as an attribute for 'container', we
     *     can rewrite our element thus:
     *     @code
     *     array(
     *       '#theme' => 'image',
     *       '#attributes' => array('class' => 'foo'),
     *       '#theme_wrappers' => array(
     *         'container' => array(
     *           '#attributes' => array('class' => 'bar'),
     *         ),
     *       ),
     *     );
     *     @endcode
     *   - If this element has an array of #post_render functions defined, they are
     *     called sequentially to modify the rendered #children. Unlike #pre_render
     *     functions, #post_render functions are passed both the rendered #children
     *     attribute as a string and the element itself.
     *   - If this element has #prefix and/or #suffix defined, they are concatenated
     *     to #children.
     *   - If this element has #cache defined, the rendered output of this element
     *     is saved to drupal_render()'s internal cache.
     *   - #printed is set to TRUE for this element to ensure that it is only
     *     rendered once.
     *   - The final value of #children for this element is returned as the rendered
     *     output.
     *
     * @param array $elements
     *   The structured array describing the data to be rendered.
     *
     * @return string
     *   The rendered HTML.
     *
     * @see element_info()
     * @see theme()
     * @see drupal_process_states()
     * @see drupal_process_attached()
     */
    function drupal_render(&$elements) {
      // Early-return nothing if user does not have access.
      if (empty($elements) || (isset($elements['#access']) && !$elements['#access'])) {
        return '';
      }
    
      // Do not print elements twice.
      if (!empty($elements['#printed'])) {
        return '';
      }
    
      // Try to fetch the element's markup from cache and return.
      if (isset($elements['#cache'])) {
        $cached_output = drupal_render_cache_get($elements);
        if ($cached_output !== FALSE) {
          return $cached_output;
        }
      }
    
      // If the default values for this element have not been loaded yet, populate
      // them.
      if (isset($elements['#type']) && empty($elements['#defaults_loaded'])) {
        $elements += element_info($elements['#type']);
      }
    
      // Make any final changes to the element before it is rendered. This means
      // that the $element or the children can be altered or corrected before the
      // element is rendered into the final text.
      if (isset($elements['#pre_render'])) {
        foreach ($elements['#pre_render'] as $callable) {
          $elements = call_user_func($callable, $elements);
        }
      }
    
      // Allow #pre_render to abort rendering.
      if (!empty($elements['#printed'])) {
        return '';
      }
    
      // Get the children of the element, sorted by weight.
      $children = element_children($elements, TRUE);
    
      // Initialize this element's #children, unless a #pre_render callback already
      // preset #children.
      if (!isset($elements['#children'])) {
        $elements['#children'] = '';
      }
    
      // Assume that if #theme is set it represents an implemented hook.
      $theme_is_implemented = isset($elements['#theme']);
    
      // Call the element's #theme function if it is set. Then any children of the
      // element have to be rendered there. If the internal #render_children
      // property is set, do not call the #theme function to prevent infinite
      // recursion.
      if ($theme_is_implemented && !isset($elements['#render_children'])) {
        $elements['#children'] = theme($elements['#theme'], $elements);
    
        // If theme() returns FALSE this means that the hook in #theme was not found
        // in the registry and so we need to update our flag accordingly. This is
        // common for theme suggestions.
        $theme_is_implemented = ($elements['#children'] !== FALSE);
      }
    
      // If #theme is not implemented or #render_children is set and the element has
      // an empty #children attribute, render the children now. This is the same
      // process as drupal_render_children() but is inlined for speed.
      if ((!$theme_is_implemented || isset($elements['#render_children'])) && empty($elements['#children'])) {
        foreach ($children as $key) {
          $elements['#children'] .= drupal_render($elements[$key]);
        }
      }
    
      // If #theme is not implemented and the element has raw #markup as a
      // fallback, prepend the content in #markup to #children. In this case
      // #children will contain whatever is provided by #pre_render prepended to
      // what is rendered recursively above. If #theme is implemented then it is
      // the responsibility of that theme implementation to render #markup if
      // required. Eventually #theme_wrappers will expect both #markup and
      // #children to be a single string as #children.
      if (!$theme_is_implemented && isset($elements['#markup'])) {
        $elements['#children'] = $elements['#markup'] . $elements['#children'];
      }
    
      // Add any JavaScript state information associated with the element.
      if (!empty($elements['#states'])) {
        drupal_process_states($elements);
      }
    
      // Add additional libraries, CSS, JavaScript an other custom
      // attached data associated with this element.
      if (!empty($elements['#attached'])) {
        drupal_process_attached($elements);
      }
    
      // Let the theme functions in #theme_wrappers add markup around the rendered
      // children.
      // #states and #attached have to be processed before #theme_wrappers, because
      // the #type 'page' render array from drupal_render_page() would render the
      // $page and wrap it into the html.tpl.php template without the attached
      // assets otherwise.
      // If the internal #render_children property is set, do not call the
      // #theme_wrappers function(s) to prevent infinite recursion.
      if (isset($elements['#theme_wrappers']) && !isset($elements['#render_children'])) {
        foreach ($elements['#theme_wrappers'] as $key => $value) {
          // If the value of a #theme_wrappers item is an array then the theme hook
          // is found in the key of the item and the value contains attribute
          // overrides. Attribute overrides replace key/value pairs in $elements for
          // only this theme() call. This allows #theme hooks and #theme_wrappers
          // hooks to share variable names without conflict or ambiguity.
          $wrapper_elements = $elements;
          if (is_string($key)) {
            $wrapper_hook = $key;
            foreach ($value as $attribute => $override) {
              $wrapper_elements[$attribute] = $override;
            }
          }
          else {
            $wrapper_hook = $value;
          }
    
          $elements['#children'] = theme($wrapper_hook, $wrapper_elements);
        }
      }
    
      // Filter the outputted content and make any last changes before the
      // content is sent to the browser. The changes are made on $content
      // which allows the output'ed text to be filtered.
      if (isset($elements['#post_render'])) {
        foreach ($elements['#post_render'] as $callable) {
          $elements['#children'] = call_user_func($callable, $elements['#children'], $elements);
        }
      }
    
      $prefix = isset($elements['#prefix']) ? $elements['#prefix'] : '';
      $suffix = isset($elements['#suffix']) ? $elements['#suffix'] : '';
      $output = $prefix . $elements['#children'] . $suffix;
    
      // Cache the processed element if #cache is set.
      if (isset($elements['#cache'])) {
        drupal_render_cache_set($output, $elements);
      }
    
      $elements['#printed'] = TRUE;
      return $output;
    }
    
    /**
     * Renders children of an element and concatenates them.
     *
     * This renders all children of an element using drupal_render() and then
     * joins them together into a single string.
     *
     * @param $element
     *   The structured array whose children shall be rendered.
     * @param $children_keys
     *   If the keys of the element's children are already known, they can be passed
     *   in to save another run of element_children().
     */
    function drupal_render_children(&$element, $children_keys = NULL) {
      if ($children_keys === NULL) {
        $children_keys = element_children($element);
      }
      $output = '';
      foreach ($children_keys as $key) {
        if (!empty($element[$key])) {
          $output .= drupal_render($element[$key]);
        }
      }
      return $output;
    }
    
    /**
     * Renders an element.
     *
     * This function renders an element using drupal_render(). The top level
     * element is shown with show() before rendering, so it will always be rendered
     * even if hide() had been previously used on it.
     *
     * @param $element
     *   The element to be rendered.
     *
     * @return
     *   The rendered element.
     *
     * @see drupal_render()
     * @see show()
     * @see hide()
     */
    function render(&$element) {
      if (!$element && $element !== 0) {
        return NULL;
      }
      if (is_array($element)) {
        show($element);
        return drupal_render($element);
      }
      else {
        // Safe-guard for inappropriate use of render() on flat variables: return
        // the variable as-is.
        return $element;
      }
    }
    
    /**
     * Hides an element from later rendering.
     *
     * The first time render() or drupal_render() is called on an element tree,
     * as each element in the tree is rendered, it is marked with a #printed flag
     * and the rendered children of the element are cached. Subsequent calls to
     * render() or drupal_render() will not traverse the child tree of this element
     * again: they will just use the cached children. So if you want to hide an
     * element, be sure to call hide() on the element before its parent tree is
     * rendered for the first time, as it will have no effect on subsequent
     * renderings of the parent tree.
     *
     * @param $element
     *   The element to be hidden.
     *
     * @return
     *   The element.
     *
     * @see render()
     * @see show()
     */
    function hide(&$element) {
      $element['#printed'] = TRUE;
      return $element;
    }
    
    /**
     * Shows a hidden element for later rendering.
     *
     * You can also use render($element), which shows the element while rendering
     * it.
     *
     * The first time render() or drupal_render() is called on an element tree,
     * as each element in the tree is rendered, it is marked with a #printed flag
     * and the rendered children of the element are cached. Subsequent calls to
     * render() or drupal_render() will not traverse the child tree of this element
     * again: they will just use the cached children. So if you want to show an
     * element, be sure to call show() on the element before its parent tree is
     * rendered for the first time, as it will have no effect on subsequent
     * renderings of the parent tree.
     *
     * @param $element
     *   The element to be shown.
     *
     * @return
     *   The element.
     *
     * @see render()
     * @see hide()
     */
    function show(&$element) {
      $element['#printed'] = FALSE;
      return $element;
    }
    
    /**
     * Gets the rendered output of a renderable element from the cache.
     *
     * @param $elements
     *   A renderable array.
     *
     * @return
     *   A markup string containing the rendered content of the element, or FALSE
     *   if no cached copy of the element is available.
     *
     * @see drupal_render()
     * @see drupal_render_cache_set()
     */
    function drupal_render_cache_get($elements) {
      if (!Drupal::request()->isMethodSafe() || !$cid = drupal_render_cid_create($elements)) {
        return FALSE;
      }
      $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'cache';
    
      if (!empty($cid) && $cache = cache($bin)->get($cid)) {
        // Add additional libraries, JavaScript, CSS and other data attached
        // to this element.
        if (isset($cache->data['#attached'])) {
          drupal_process_attached($cache->data);
        }
        // Return the rendered output.
        return $cache->data['#markup'];
      }
      return FALSE;
    }
    
    /**
     * Caches the rendered output of a renderable element.
     *
     * This is called by drupal_render() if the #cache property is set on an
     * element.
     *
     * @param $markup
     *   The rendered output string of $elements.
     * @param $elements
     *   A renderable array.
     *
     * @see drupal_render_cache_get()
     */
    function drupal_render_cache_set(&$markup, $elements) {
      // Create the cache ID for the element.
      if (!Drupal::request()->isMethodSafe() || !$cid = drupal_render_cid_create($elements)) {
        return FALSE;
      }
    
      // Cache implementations are allowed to modify the markup, to support
      // replacing markup with edge-side include commands. The supporting cache
      // backend will store the markup in some other key (like
      // $data['#real-value']) and return an include command instead. When the
      // ESI command is executed by the content accelerator, the real value can
      // be retrieved and used.
      $data['#markup'] = &$markup;
      // Persist attached data associated with this element.
      $attached = drupal_render_collect_attached($elements, TRUE);
      if ($attached) {
        $data['#attached'] = $attached;
      }
      $bin = isset($elements['#cache']['bin']) ? $elements['#cache']['bin'] : 'cache';
      $expire = isset($elements['#cache']['expire']) ? $elements['#cache']['expire'] : CacheBackendInterface::CACHE_PERMANENT;
      $tags = isset($elements['#cache']['tags']) ? $elements['#cache']['tags'] : array();
      cache($bin)->set($cid, $data, $expire, $tags);
    }
    
    /**
     * Collects #attached for an element and its children into a single array.
     *
     * When caching elements, it is necessary to collect all libraries, JavaScript
     * and CSS into a single array, from both the element itself and all child
     * elements. This allows drupal_render() to add these back to the page when the
     * element is returned from cache.
     *
     * @param $elements
     *   The element to collect #attached from.
     * @param $return
     *   Whether to return the attached elements and reset the internal static.
     *
     * @return
     *   The #attached array for this element and its descendants.
     */
    function drupal_render_collect_attached($elements, $return = FALSE) {
      $attached = &drupal_static(__FUNCTION__, array());
    
      // Collect all #attached for this element.
      if (isset($elements['#attached'])) {
        foreach ($elements['#attached'] as $key => $value) {
          if (!isset($attached[$key])) {
            $attached[$key] = array();
          }
          $attached[$key] = array_merge($attached[$key], $value);
        }
      }
      if ($children = element_children($elements)) {
        foreach ($children as $child) {
          drupal_render_collect_attached($elements[$child]);
        }
      }
    
      // If this was the first call to the function, return all attached elements
      // and reset the static cache.
      if ($return) {
        $return = $attached;
        $attached = array();
        return $return;
      }
    }
    
    /**
     * Prepares an element for caching based on a query.
     *
     * This smart caching strategy saves Drupal from querying and rendering to HTML
     * when the underlying query is unchanged.
     *
     * Expensive queries should use the query builder to create the query and then
     * call this function. Executing the query and formatting results should happen
     * in a #pre_render callback.
     *
     * @param $query
     *   A select query object as returned by db_select().
     * @param $function
     *   The name of the function doing this caching. A _pre_render suffix will be
     *   added to this string and is also part of the cache key in
     *   drupal_render_cache_set() and drupal_render_cache_get().
     * @param $expire
     *   The cache expire time, passed eventually to cache()->set().
     * @param $granularity
     *   One or more granularity constants passed to drupal_render_cid_parts().
     *
     * @return
     *   A renderable array with the following keys and values:
     *   - #query: The passed-in $query.
     *   - #pre_render: $function with a _pre_render suffix.
     *   - #cache: An associative array prepared for drupal_render_cache_set().
     */
    function drupal_render_cache_by_query($query, $function, $expire = CacheBackendInterface::CACHE_PERMANENT, $granularity = NULL) {
      $cache_keys = array_merge(array($function), drupal_render_cid_parts($granularity));
      $query->preExecute();
      $cache_keys[] = hash('sha256', serialize(array((string) $query, $query->getArguments())));
      return array(
        '#query' => $query,
        '#pre_render' => array($function . '_pre_render'),
        '#cache' => array(
          'keys' => $cache_keys,
          'expire' => $expire,
        ),
      );
    }
    
    /**
     * Returns cache ID parts for building a cache ID.
     *
     * @param $granularity
     *   One or more cache granularity constants. For example, to cache separately
     *   for each user, use DRUPAL_CACHE_PER_USER. To cache separately for each
     *   page and role, use the expression:
     *   @code
     *   DRUPAL_CACHE_PER_PAGE | DRUPAL_CACHE_PER_ROLE
     *   @endcode
     *
     * @return
     *   An array of cache ID parts, always containing the active theme. If the
     *   locale module is enabled it also contains the active language. If
     *   $granularity was passed in, more parts are added.
     */
    function drupal_render_cid_parts($granularity = NULL) {
      global $theme, $base_root, $user;
    
      $cid_parts[] = $theme;
      // If Locale is enabled but we have only one language we do not need it as cid
      // part.
      if (language_multilingual()) {
        foreach (language_types_get_configurable() as $language_type) {
          $cid_parts[] = language($language_type)->id;
        }
      }
    
      if (!empty($granularity)) {
        // 'PER_ROLE' and 'PER_USER' are mutually exclusive. 'PER_USER' can be a
        // resource drag for sites with many users, so when a module is being
        // equivocal, we favor the less expensive 'PER_ROLE' pattern.
        if ($granularity & DRUPAL_CACHE_PER_ROLE) {
          $cid_parts[] = 'r.' . implode(',', $user->getRoles());
        }
        elseif ($granularity & DRUPAL_CACHE_PER_USER) {
          $cid_parts[] = 'u.' . $user->id();
        }
    
        if ($granularity & DRUPAL_CACHE_PER_PAGE) {
          $cid_parts[] = $base_root . request_uri();
        }
      }
    
      return $cid_parts;
    }
    
    /**
     * Creates the cache ID for a renderable element.
     *
     * This creates the cache ID string, either by returning the #cache['cid']
     * property if present or by building the cache ID out of the #cache['keys']
     * and, optionally, the #cache['granularity'] properties.
     *
     * @param $elements
     *   A renderable array.
     *
     * @return
     *   The cache ID string, or FALSE if the element may not be cached.
     */
    function drupal_render_cid_create($elements) {
      if (isset($elements['#cache']['cid'])) {
        return $elements['#cache']['cid'];
      }
      elseif (isset($elements['#cache']['keys'])) {
        $granularity = isset($elements['#cache']['granularity']) ? $elements['#cache']['granularity'] : NULL;
        // Merge in additional cache ID parts based provided by drupal_render_cid_parts().
        $cid_parts = array_merge($elements['#cache']['keys'], drupal_render_cid_parts($granularity));
        return implode(':', $cid_parts);
      }
      return FALSE;
    }
    
    /**
     * Sorts a structured array by '#weight' property.
     *
     * Callback for uasort() within element_children().
     *
     * @param $a
     *   First item for comparison. The compared items should be associative arrays
     *   that optionally include a '#weight' key.
     * @param $b
     *   Second item for comparison.
     *
     * @return int
     *   The comparison result for uasort().
     *
     * @see \Drupal\Component\Utility\SortArray::sortByWeightProperty()
     *
     * @deprecated as of Drupal 8.0. Use SortArray::sortByWeightProperty() instead.
     */
    function element_sort($a, $b) {
      return SortArray::sortByWeightProperty($a, $b);
    }
    
    /**
     * Sorts a structured array by '#title' property.
     *
     * Callback for uasort() within:
     * - system_modules()
     * - theme_simpletest_test_table()
     *
     * @param $a
     *   First item for comparison. The compared items should be associative arrays
     *   that optionally include a '#title' key.
     * @param $b
     *   Second item for comparison.
     *
     * @return int
     *   The comparison result for uasort().
     *
     * @see \Drupal\Component\Utility\SortArray::sortByTitleProperty()
     *
     * @deprecated as of Drupal 8.0. Use SortArray::sortByTitleProperty() instead.
     */
    function element_sort_by_title($a, $b) {
      return SortArray::sortByTitleProperty($a, $b);
    }
    
    /**
     * Retrieves the default properties for the defined element type.
     *
     * @param $type
     *   An element type as defined by hook_element_info().
     */
    function element_info($type) {
      // Use the advanced drupal_static() pattern, since this is called very often.
      static $drupal_static_fast;
      if (!isset($drupal_static_fast)) {
        $drupal_static_fast['cache'] = &drupal_static(__FUNCTION__);
      }
      $cache = &$drupal_static_fast['cache'];
    
      if (!isset($cache)) {
        $cache = Drupal::moduleHandler()->invokeAll('element_info');
        foreach ($cache as $element_type => $info) {
          $cache[$element_type]['#type'] = $element_type;
        }
        // Allow modules to alter the element type defaults.
        drupal_alter('element_info', $cache);
      }
    
      return isset($cache[$type]) ? $cache[$type] : array();
    }
    
    /**
     * Retrieves a single property for the defined element type.
     *
     * @param $type
     *   An element type as defined by hook_element_info().
     * @param $property_name
     *   The property within the element type that should be returned.
     * @param $default
     *   (Optional) The value to return if the element type does not specify a
     *   value for the property. Defaults to NULL.
     */
    function element_info_property($type, $property_name, $default = NULL) {
      return (($info = element_info($type)) && array_key_exists($property_name, $info)) ? $info[$property_name] : $default;
    }
    
    /**
     * Sorts a structured array by the 'weight' element.
     *
     * Note that the sorting is by the 'weight' array element, not by the render
     * element property '#weight'.
     *
     * Callback for uasort() used in various functions.
     *
     * @param $a
     *   First item for comparison. The compared items should be associative arrays
     *   that optionally include a 'weight' element. For items without a 'weight'
     *   element, a default value of 0 will be used.
     * @param $b
     *   Second item for comparison.
     *
     * @return int
     *   The comparison result for uasort().
     *
     * @see \Drupal\Component\Utility\SortArray::sortByWeightElement()
     *
     * @deprecated as of Drupal 8.0. Use SortArray::sortByWeightElement() instead.
     */
    function drupal_sort_weight($a, $b) {
      return SortArray::sortByWeightElement((array) $a, (array) $b);
    }
    
    /**
     * Sorts a structured array by 'title' key (no # prefix).
     *
     * Callback for uasort() within system_admin_index().
     *
     * @param $a
     *   First item for comparison. The compared items should be associative arrays
     *   that optionally include a 'title' key.
     * @param $b
     *   Second item for comparison.
     *
     * @return int
     *   The comparison result for uasort().
     *
     * @see \Drupal\Component\Utility\SortArray::sortByTitleElement()
     *
     * @deprecated as of Drupal 8.0. Use SortArray::sortByTitleElement() instead.
     */
    function drupal_sort_title($a, $b) {
      return SortArray::sortByTitleElement($a, $b);
    }
    
    /**
     * Checks if the key is a property.
     */
    function element_property($key) {
      return $key[0] == '#';
    }
    
    /**
     * Gets properties of a structured array element (keys beginning with '#').
     */
    function element_properties($element) {
      return array_filter(array_keys((array) $element), 'element_property');
    }
    
    /**
     * Checks if the key is a child.
     */
    function element_child($key) {
      return !isset($key[0]) || $key[0] != '#';
    }
    
    /**
     * Identifies the children of an element array, optionally sorted by weight.
     *
     * The children of a element array are those key/value pairs whose key does
     * not start with a '#'. See drupal_render() for details.
     *
     * @param $elements
     *   The element array whose children are to be identified.
     * @param $sort
     *   Boolean to indicate whether the children should be sorted by weight.
     *
     * @return
     *   The array keys of the element's children.
     */
    function element_children(&$elements, $sort = FALSE) {
      // Do not attempt to sort elements which have already been sorted.
      $sort = isset($elements['#sorted']) ? !$elements['#sorted'] : $sort;
    
      // Filter out properties from the element, leaving only children.
      $children = array();
      $sortable = FALSE;
      foreach ($elements as $key => $value) {
        if ($key === '' || $key[0] !== '#') {
          if (is_array($value)) {
            $children[$key] = $value;
            if (isset($value['#weight'])) {
              $sortable = TRUE;
            }
          }
          // Only trigger an error if the value is not null.
          // @see http://drupal.org/node/1283892
          elseif (isset($value)) {
            trigger_error(t('"@key" is an invalid render array key', array('@key' => $key)), E_USER_ERROR);
          }
        }
      }
      // Sort the children if necessary.
      if ($sort && $sortable) {
        uasort($children, 'element_sort');
        // Put the sorted children back into $elements in the correct order, to
        // preserve sorting if the same element is passed through
        // element_children() twice.
        foreach ($children as $key => $child) {
          unset($elements[$key]);
          $elements[$key] = $child;
        }
        $elements['#sorted'] = TRUE;
      }
    
      return array_keys($children);
    }
    
    /**
     * Returns the visible children of an element.
     *
     * @param $elements
     *   The parent element.
     *
     * @return
     *   The array keys of the element's visible children.
     */
    function element_get_visible_children(array $elements) {
      $visible_children = array();
    
      foreach (element_children($elements) as $key) {
        $child = $elements[$key];
    
        // Skip un-accessible children.
        if (isset($child['#access']) && !$child['#access']) {
          continue;
        }
    
        // Skip value and hidden elements, since they are not rendered.
        if (isset($child['#type']) && in_array($child['#type'], array('value', 'hidden'))) {
          continue;
        }
    
        $visible_children[$key] = $child;
      }
    
      return array_keys($visible_children);
    }
    
    /**
     * Sets HTML attributes based on element properties.
     *
     * @param $element
     *   The renderable element to process.
     * @param $map
     *   An associative array whose keys are element property names and whose values
     *   are the HTML attribute names to set for corresponding the property; e.g.,
     *   array('#propertyname' => 'attributename'). If both names are identical
     *   except for the leading '#', then an attribute name value is sufficient and
     *   no property name needs to be specified.
     */
    function element_set_attributes(array &$element, array $map) {
      foreach ($map as $property => $attribute) {
        // If the key is numeric, the attribute name needs to be taken over.
        if (is_int($property)) {
          $property = '#' . $attribute;
        }
        // Do not overwrite already existing attributes.
        if (isset($element[$property]) && !isset($element['#attributes'][$attribute])) {
          $element['#attributes'][$attribute] = $element[$property];
        }
      }
    }
    
    /**
     * Parses Drupal module and theme .info.yml files.
     *
     * Info files are NOT for placing arbitrary theme and module-specific settings.
     * Use Config::get() and Config::set()->save() for that. Info files are
     * formatted as YAML. If the 'version' key is set to 'VERSION' in any info file,
     * then the value will be substituted with the current version of Drupal core.
     *
     * Information stored in a module .info.yml file:
     * - name: The real name of the module for display purposes.
     * - description: A brief description of the module.
     * - dependencies: An array of shortnames of other modules this module requires.
     * - package: The name of the package of modules this module belongs to.
     *
     * See forum.info.yml for an example of a module .info.yml file.
     *
     * Information stored in a theme .info.yml file:
     * - name: The real name of the theme for display purposes.
     * - description: Brief description.
     * - screenshot: Path to screenshot relative to the theme's .info.yml file.
     * - engine: Theme engine; typically twig.
     * - base theme: Name of a base theme, if applicable.
     * - regions: Listed regions.
     * - features: Features available.
     * - stylesheets: Theme stylesheets.
     * - scripts: Theme scripts.
     *
     * See bartik.info.yml for an example of a theme .info.yml file.
     *
     * @param string $filename
     *   The file we are parsing. Accepts file with relative or absolute path.
     *
     * @return array
     *   The info array.
     */
    function drupal_parse_info_file($filename) {
      static $info = array();
    
      if (!isset($info[$filename])) {
        if (!file_exists($filename)) {
          $info[$filename] = array();
        }
        else {
          $parser = new Parser();
          $info[$filename] = $parser->parse(file_get_contents($filename));
          if (isset($info[$filename]['version']) && $info[$filename]['version'] === 'VERSION') {
            $info[$filename]['version'] = Drupal::VERSION;
          }
        }
      }
      return $info[$filename];
    }
    
    /**
     * Returns a list of severity levels, as defined in RFC 3164.
     *
     * @return
     *   Array of the possible severity levels for log messages.
     *
     * @see http://www.ietf.org/rfc/rfc3164.txt
     * @see watchdog()
     * @ingroup logging_severity_levels
     */
    function watchdog_severity_levels() {
      return array(
        WATCHDOG_EMERGENCY   => t('Emergency'),
        WATCHDOG_ALERT   => t('Alert'),
        WATCHDOG_CRITICAL    => t('Critical'),
        WATCHDOG_ERROR     => t('Error'),
        WATCHDOG_WARNING => t('Warning'),
        WATCHDOG_NOTICE  => t('Notice'),
        WATCHDOG_INFO    => t('Info'),
        WATCHDOG_DEBUG   => t('Debug'),
      );
    }
    
    
    /**
     * Explodes a string of tags into an array.
     *
     * @see drupal_implode_tags()
     * @see \Drupal\Component\Utility\String::explodeTags().
     *
     * @deprecated as of Drupal 8.0. Use Tags::explode() instead.
     */
    function drupal_explode_tags($tags) {
      return Tags::explode($tags);
    }
    
    /**
     * Implodes an array of tags into a string.
     *
     * @see drupal_explode_tags()
     * @see \Drupal\Component\Utility\String::implodeTags().
     *
     * @deprecated as of Drupal 8.0. Use Tags::implode() instead.
     */
    function drupal_implode_tags($tags) {
      return Tags::implode($tags);
    }
    
    /**
     * Flushes all persistent caches, resets all variables, and rebuilds all data structures.
     *
     * At times, it is necessary to re-initialize the entire system to account for
     * changed or new code. This function:
     * - Clears all persistent caches:
     *   - The bootstrap cache bin containing base system, module system, and theme
     *     system information.
     *   - The common 'cache' cache bin containing arbitrary caches.
     *   - The page cache.
     *   - The URL alias path cache.
     * - Resets all static variables that have been defined via drupal_static().
     * - Clears asset (JS/CSS) file caches.
     * - Updates the system with latest information about extensions (modules and
     *   themes).
     * - Updates the bootstrap flag for modules implementing bootstrap_hooks().
     * - Rebuilds the full database schema information (invoking hook_schema()).
     * - Rebuilds data structures of all modules (invoking hook_rebuild()). In
     *   core this means
     *   - blocks, node types, date formats and actions are synchronized with the
     *     database
     *   - The 'active' status of fields is refreshed.
     * - Rebuilds the menu router.
     *
     * This means the entire system is reset so all caches and static variables are
     * effectively empty. After that is guaranteed, information about the currently
     * active code is updated, and rebuild operations are successively called in
     * order to synchronize the active system according to the current information
     * defined in code.
     *
     * All modules need to ensure that all of their caches are flushed when
     * hook_cache_flush() is invoked; any previously known information must no
     * longer exist. All following hook_rebuild() operations must be based on fresh
     * and current system data. All modules must be able to rely on this contract.
     *
     * @see \Drupal\Core\Cache\CacheHelper::getBins()
     * @see hook_cache_flush()
     * @see hook_rebuild()
     *
     * This function also resets the theme, which means it is not initialized
     * anymore and all previously added JavaScript and CSS is gone. Normally, this
     * function is called as an end-of-POST-request operation that is followed by a
     * redirect, so this effect is not visible. Since the full reset is the whole
     * point of this function, callers need to take care for backing up all needed
     * variables and properly restoring or re-initializing them on their own. For
     * convenience, this function automatically re-initializes the maintenance theme
     * if it was initialized before.
     *
     * @todo Try to clear page/JS/CSS caches last, so cached pages can still be
     *   served during this possibly long-running operation. (Conflict on bootstrap
     *   cache though.)
     * @todo Add a global lock to ensure that caches are not primed in concurrent
     *   requests.
     */
    function drupal_flush_all_caches() {
      $module_handler = Drupal::moduleHandler();
      // Flush all persistent caches.
      // This is executed based on old/previously known information, which is
      // sufficient, since new extensions cannot have any primed caches yet.
      $module_handler->invokeAll('cache_flush');
      foreach (Cache::getBins() as $service_id => $cache_backend) {
        if ($service_id != 'cache.menu') {
          $cache_backend->deleteAll();
        }
      }
    
      // Flush asset file caches.
      drupal_clear_css_cache();
      drupal_clear_js_cache();
      _drupal_flush_css_js();
    
      // Reset all static caches.
      drupal_static_reset();
    
      // Clear all non-drupal_static() static caches.
      Drupal::entityManager()->clearCachedDefinitions();
    
      // Wipe the PHP Storage caches.
      PhpStorageFactory::get('service_container')->deleteAll();
      PhpStorageFactory::get('twig')->deleteAll();
    
      // Rebuild module and theme data.
      $module_data = system_rebuild_module_data();
      system_rebuild_theme_data();
    
      // Rebuild and reboot a new kernel. A simple DrupalKernel reboot is not
      // sufficient, since the list of enabled modules might have been adjusted
      // above due to changed code.
      $files = array();
      foreach ($module_data as $module => $data) {
        if (isset($data->uri) && $data->status) {
          $files[$module] = $data->uri;
        }
      }
      Drupal::service('kernel')->updateModules($module_handler->getModuleList(), $files);
      // New container, new module handler.
      $module_handler = Drupal::moduleHandler();
    
      // Ensure that all modules that are currently supposed to be enabled are
      // actually loaded.
      $module_handler->loadAll();
    
      // Rebuild the schema and cache a fully-built schema based on new module data.
      // This is necessary for any invocation of index.php, because setting cache
      // table entries requires schema information and that occurs during bootstrap
      // before any modules are loaded, so if there is no cached schema,
      // drupal_get_schema() will try to generate one, but with no loaded modules,
      // it will return nothing.
      drupal_get_schema(NULL, TRUE);
    
      // Rebuild all information based on new module data.
      $module_handler->invokeAll('rebuild');
    
      // Rebuild the menu router based on all rebuilt data.
      // Important: This rebuild must happen last, so the menu router is guaranteed
      // to be based on up to date information.
      Drupal::service('router.builder')->rebuild();
      menu_router_rebuild();
    
      // Re-initialize the maintenance theme, if the current request attempted to
      // use it. Unlike regular usages of this function, the installer and update
      // scripts need to flush all caches during GET requests/page building.
      if (function_exists('_drupal_maintenance_theme')) {
        unset($GLOBALS['theme']);
        drupal_maintenance_theme();
      }
    }
    
    /**
     * Changes the dummy query string added to all CSS and JavaScript files.
     *
     * Changing the dummy query string appended to CSS and JavaScript files forces
     * all browsers to reload fresh files.
     */
    function _drupal_flush_css_js() {
      // The timestamp is converted to base 36 in order to make it more compact.
      variable_set('css_js_query_string', base_convert(REQUEST_TIME, 10, 36));
    }
    
    /**
     * Outputs debug information.
     *
     * The debug information is passed on to trigger_error() after being converted
     * to a string using _drupal_debug_message().
     *
     * @param $data
     *   Data to be output.
     * @param $label
     *   Label to prefix the data.
     * @param $print_r
     *   Flag to switch between print_r() and var_export() for data conversion to
     *   string. Set $print_r to TRUE when dealing with a recursive data structure
     *   as var_export() will generate an error.
     */
    function debug($data, $label = NULL, $print_r = FALSE) {
      // Print $data contents to string.
      $string = check_plain($print_r ? print_r($data, TRUE) : var_export($data, TRUE));
    
      // Display values with pre-formatting to increase readability.
      $string = '<pre>' . $string . '</pre>';
    
      trigger_error(trim($label ? "$label: $string" : $string));
    }
    
    /**
     * Checks whether a version is compatible with a given dependency.
     *
     * @param $v
     *   A parsed dependency structure e.g. from ModuleHandler::parseDependency().
     * @param $current_version
     *   The version to check against (like 4.2).
     *
     * @return
     *   NULL if compatible, otherwise the original dependency version string that
     *   caused the incompatibility.
     *
     * @see \Drupal\Core\Extension\ModuleHandler::parseDependency()
     */
    function drupal_check_incompatibility($v, $current_version) {
      if (!empty($v['versions'])) {
        foreach ($v['versions'] as $required_version) {
          if ((isset($required_version['op']) && !version_compare($current_version, $required_version['version'], $required_version['op']))) {
            return $v['original_version'];
          }
        }
      }
    }
    
    /**
     * Returns a string of supported archive extensions.
     *
     * @return
     *   A space-separated string of extensions suitable for use by the file
     *   validation system.
     */
    function archiver_get_extensions() {
      $valid_extensions = array();
      foreach (Drupal::service('plugin.manager.archiver')->getDefinitions() as $archive) {
        foreach ($archive['extensions'] as $extension) {
          foreach (explode('.', $extension) as $part) {
            if (!in_array($part, $valid_extensions)) {
              $valid_extensions[] = $part;
            }
          }
        }
      }
      return implode(' ', $valid_extensions);
    }
    
    /**
     * Creates the appropriate archiver for the specified file.
     *
     * @param $file
     *   The full path of the archive file. Note that stream wrapper paths are
     *   supported, but not remote ones.
     *
     * @return
     *   A newly created instance of the archiver class appropriate
     *   for the specified file, already bound to that file.
     *   If no appropriate archiver class was found, will return FALSE.
     */
    function archiver_get_archiver($file) {
      // Archivers can only work on local paths
      $filepath = drupal_realpath($file);
      if (!is_file($filepath)) {
        throw new Exception(t('Archivers can only operate on local files: %file not supported', array('%file' => $file)));
      }
      return Drupal::service('plugin.manager.archiver')->getInstance(array('filepath' => $filepath));
    }
    
    /**
     * Assembles the Drupal Updater registry.
     *
     * An Updater is a class that knows how to update various parts of the Drupal
     * file system, for example to update modules that have newer releases, or to
     * install a new theme.
     *
     * @return array
     *   The Drupal Updater class registry.
     *
     * @see Drupal\Core\Updater\Updater
     * @see hook_updater_info()
     * @see hook_updater_info_alter()
     */
    function drupal_get_updaters() {
      $updaters = &drupal_static(__FUNCTION__);
      if (!isset($updaters)) {
        $updaters = Drupal::moduleHandler()->invokeAll('updater_info');
        drupal_alter('updater_info', $updaters);
        uasort($updaters, 'drupal_sort_weight');
      }
      return $updaters;
    }
    
    /**
     * Assembles the Drupal FileTransfer registry.
     *
     * @return
     *   The Drupal FileTransfer class registry.
     *
     * @see Drupal\Core\FileTransfer\FileTransfer
     * @see hook_filetransfer_info()
     * @see hook_filetransfer_info_alter()
     */
    function drupal_get_filetransfer_info() {
      $info = &drupal_static(__FUNCTION__);
      if (!isset($info)) {
        $info = Drupal::moduleHandler()->invokeAll('filetransfer_info');
        drupal_alter('filetransfer_info', $info);
        uasort($info, 'drupal_sort_weight');
      }
      return $info;
    }
    
    /**
     * @defgroup queue Queue operations
     * @{
     * Queue items to allow later processing.
     *
     * The queue system allows placing items in a queue and processing them later.
     * The system tries to ensure that only one consumer can process an item.
     *
     * Before a queue can be used it needs to be created by
     * Drupal\Core\Queue\QueueInterface::createQueue().
     *
     * Items can be added to the queue by passing an arbitrary data object to
     * Drupal\Core\Queue\QueueInterface::createItem().
     *
     * To process an item, call Drupal\Core\Queue\QueueInterface::claimItem() and
     * specify how long you want to have a lease for working on that item.
     * When finished processing, the item needs to be deleted by calling
     * Drupal\Core\Queue\QueueInterface::deleteItem(). If the consumer dies, the
     * item will be made available again by the Drupal\Core\Queue\QueueInterface
     * implementation once the lease expires. Another consumer will then be able to
     * receive it when calling Drupal\Core\Queue\QueueInterface::claimItem().
     * Due to this, the processing code should be aware that an item might be handed
     * over for processing more than once.
     *
     * The $item object used by the Drupal\Core\Queue\QueueInterface can contain
     * arbitrary metadata depending on the implementation. Systems using the
     * interface should only rely on the data property which will contain the
     * information passed to Drupal\Core\Queue\QueueInterface::createItem().
     * The full queue item returned by Drupal\Core\Queue\QueueInterface::claimItem()
     * needs to be passed to Drupal\Core\Queue\QueueInterface::deleteItem() once
     * processing is completed.
     *
     * There are two kinds of queue backends available: reliable, which preserves
     * the order of messages and guarantees that every item will be executed at
     * least once. The non-reliable kind only does a best effort to preserve order
     * in messages and to execute them at least once but there is a small chance
     * that some items get lost. For example, some distributed back-ends like
     * Amazon SQS will be managing jobs for a large set of producers and consumers
     * where a strict FIFO ordering will likely not be preserved. Another example
     * would be an in-memory queue backend which might lose items if it crashes.
     * However, such a backend would be able to deal with significantly more writes
     * than a reliable queue and for many tasks this is more important. See
     * aggregator_cron() for an example of how to effectively utilize a
     * non-reliable queue. Another example is doing Twitter statistics -- the small
     * possibility of losing a few items is insignificant next to power of the
     * queue being able to keep up with writes. As described in the processing
     * section, regardless of the queue being reliable or not, the processing code
     * should be aware that an item might be handed over for processing more than
     * once (because the processing code might time out before it finishes).
     */
    
    /**
     * @} End of "defgroup queue".
     */