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<?php

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use Drupal\Component\Utility\Crypt;
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use Drupal\Component\Utility\String;
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use Drupal\Component\Utility\Tags;
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use Drupal\Component\Utility\UrlValidator;
use Drupal\Component\Utility\Xss;
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use Drupal\Core\Cache\Cache;
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use Drupal\Core\Language\Language;
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use Symfony\Component\DependencyInjection\Container;
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use Symfony\Component\HttpFoundation\RedirectResponse;
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use Symfony\Component\Yaml\Parser;
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use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\Request;
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use Drupal\Component\PhpStorage\PhpStorageFactory;
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use Drupal\Component\Utility\MapArray;
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use Drupal\Component\Utility\NestedArray;
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use Drupal\Component\Utility\Unicode;
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use Drupal\Core\Cache\CacheBackendInterface;
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use Drupal\Core\Datetime\DrupalDateTime;
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use Drupal\Core\Database\Database;
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use Drupal\Core\Routing\GeneratorNotInitializedException;
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use Drupal\Core\SystemListingInfo;
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use Drupal\Core\Template\Attribute;
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/**
 * @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.
 */

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/**
 * @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
 *
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 * @}
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 */

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/**
 * Return status for saving which involved creating a new item.
 */
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const SAVED_NEW = 1;
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/**
 * Return status for saving which involved an update to an existing item.
 */
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const SAVED_UPDATED = 2;
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/**
 * Return status for saving which deleted an existing item.
 */
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const SAVED_DELETED = 3;
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/**
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 * The default aggregation group for CSS files added to the page.
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 */
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const CSS_AGGREGATE_DEFAULT = 0;
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/**
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 * The default aggregation group for theme CSS files added to the page.
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 */
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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;
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/**
 * The default group for JavaScript settings added to the page.
 */
const JS_SETTING = -200;

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/**
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 * The default group for JavaScript and jQuery libraries added to the page.
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 */
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const JS_LIBRARY = -100;
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/**
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 * The default group for module JavaScript code added to the page.
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 */
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const JS_DEFAULT = 0;
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/**
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 * The default group for theme JavaScript code added to the page.
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 */
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const JS_THEME = 100;
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/**
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 * @defgroup block_caching Block Caching
 * @{
 * Constants that define each block's caching state.
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 *
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 * 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.
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 *
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 * The block cache is cleared when the 'content' cache tag is invalidated,
 * following the same pattern as the page cache (node, comment, user, taxonomy
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 * added or updated...).
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 *
 * Note that user 1 is excluded from block caching.
 */

/**
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 * 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.
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 */
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const DRUPAL_NO_CACHE = -1;
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/**
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 * The block is handling its own caching in its hook_block_view().
 *
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 * This setting is useful when time based expiration is needed or a site uses a
 * node access which invalidates standard block cache.
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 */
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const DRUPAL_CACHE_CUSTOM = -2;
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/**
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 * 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.
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 */
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const DRUPAL_CACHE_PER_ROLE = 0x0001;
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/**
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 * The block or element can change depending on the user.
 *
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 * 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.
 */
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const DRUPAL_CACHE_PER_USER = 0x0002;
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/**
 * The block or element can change depending on the page being viewed.
 */
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const DRUPAL_CACHE_PER_PAGE = 0x0004;
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/**
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 * The block or element is the same for every user and page that it is visible.
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 */
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const DRUPAL_CACHE_GLOBAL = 0x0008;
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/**
 * @} End of "defgroup block_caching".
 */

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/**
 * 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";

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/**
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 * Adds content to a specified region.
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 *
 * @param $region
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 *   Page region the content is added to.
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 * @param $data
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 *   Content to be added.
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 */
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function drupal_add_region_content($region = NULL, $data = NULL) {
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  static $content = array();

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  if (isset($region) && isset($data)) {
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    $content[$region][] = $data;
  }
  return $content;
}

/**
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 * Gets assigned content for a given region.
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 *
 * @param $region
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 *   A specified region to fetch content for. If NULL, all regions will be
 *   returned.
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 * @param $delimiter
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 *   Content to be inserted between imploded array elements.
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 */
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function drupal_get_region_content($region = NULL, $delimiter = ' ') {
  $content = drupal_add_region_content();
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  if (isset($region)) {
    if (isset($content[$region]) && is_array($content[$region])) {
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      return implode($delimiter, $content[$region]);
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    }
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  }
  else {
    foreach (array_keys($content) as $region) {
      if (is_array($content[$region])) {
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        $content[$region] = implode($delimiter, $content[$region]);
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      }
    }
    return $content;
  }
}

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/**
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 * Gets the name of the currently active installation profile.
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 *
 * 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
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 * table contains the name of the current profile, and we can call
 * variable_get() to determine what one is active.
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 *
 * @return $profile
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 *   The name of the installation profile.
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 */
function drupal_get_profile() {
  global $install_state;

  if (isset($install_state['parameters']['profile'])) {
    $profile = $install_state['parameters']['profile'];
  }
  else {
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    $profile = variable_get('install_profile', 'standard');
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  }

  return $profile;
}


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/**
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 * Sets the breadcrumb trail for the current page.
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 *
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 * @param $breadcrumb
 *   Array of links, starting with "home" and proceeding up to but not including
 *   the current page.
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 *
 * @deprecated This will be removed in 8.0. Instead, register a new breadcrumb
 *   builder service.
 *
 * @see Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface
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 */
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function drupal_set_breadcrumb($breadcrumb = NULL) {
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  $stored_breadcrumb = &drupal_static(__FUNCTION__);
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  if (isset($breadcrumb)) {
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    $stored_breadcrumb = $breadcrumb;
  }
  return $stored_breadcrumb;
}

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/**
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 * Adds output to the HEAD tag of the HTML page.
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 *
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 * This function can be called as long as the headers aren't sent. Pass no
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 * 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 $data is not NULL.
 *
 * @return
 *   An array of all stored HEAD elements.
 *
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 * @see drupal_pre_render_html_tag()
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 */
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function drupal_add_html_head($data = NULL, $key = NULL) {
  $stored_head = &drupal_static(__FUNCTION__);
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  if (!isset($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;
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  }
  return $stored_head;
}

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/**
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 * 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.
  $elements['system_meta_content_type'] = array(
    '#type' => 'html_tag',
    '#tag' => 'meta',
    '#attributes' => array(
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      'charset' => 'utf-8',
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    ),
    // Security: This always has to be output first.
    '#weight' => -1000,
  );
  // Show Drupal and the major version number in the META GENERATOR tag.
  // Get the major version.
  list($version, ) = explode('.', 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;
}

/**
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 * Retrieves output to be displayed in the HEAD tag of the HTML page.
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 */
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function drupal_get_html_head() {
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  $elements = drupal_add_html_head();
  drupal_alter('html_head', $elements);
  return drupal_render($elements);
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}

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/**
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 * Adds a feed URL for the current page.
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 *
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 * This function can be called as long the HTML header hasn't been sent.
 *
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 * @param $url
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 *   An internal system path or a fully qualified external URL of the feed.
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 * @param $title
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 *   The title of the feed.
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 */
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function drupal_add_feed($url = NULL, $title = '') {
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  $stored_feed_links = &drupal_static(__FUNCTION__, array());
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  if (isset($url)) {
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    $stored_feed_links[$url] = theme('feed_icon', array('url' => $url, 'title' => $title));
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    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)),
    ));
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  }
  return $stored_feed_links;
}

/**
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 * Gets the feed URLs for the current page.
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 *
 * @param $delimiter
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 *   A delimiter to split feeds by.
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 */
function drupal_get_feeds($delimiter = "\n") {
  $feeds = drupal_add_feed();
  return implode($feeds, $delimiter);
}

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/**
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 * @defgroup http_handling HTTP handling
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 * @{
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 * Functions to properly handle HTTP responses.
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 */

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/**
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 * Processes a URL query parameter array to remove unwanted elements.
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 *
 * @param $query
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 *   (optional) An array to be processed. Defaults to $_GET.
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 * @param $exclude
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 *   (optional) A list of $query array keys to remove. Use "parent[child]" to
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 *   exclude nested items.
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 * @param $parent
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 *   Internal use only. Used to build the $query array key for nested items.
 *
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 * @return
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 *   An array containing query parameters, which can be used for url().
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 */
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function drupal_get_query_parameters(array $query = NULL, array $exclude = array(), $parent = '') {
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  // Set defaults, if none given.
  if (!isset($query)) {
    $query = $_GET;
  }
  // If $exclude is empty, there is nothing to filter.
  if (empty($exclude)) {
    return $query;
  }
  elseif (!$parent) {
    $exclude = array_flip($exclude);
  }
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  $params = array();
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  foreach ($query as $key => $value) {
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    $string_key = ($parent ? $parent . '[' . $key . ']' : $key);
    if (isset($exclude[$string_key])) {
      continue;
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    }

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    if (is_array($value)) {
      $params[$key] = drupal_get_query_parameters($value, $exclude, $string_key);
    }
    else {
      $params[$key] = $value;
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    }
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  }

  return $params;
}

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/**
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 * Splits a URL-encoded query string into an array.
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 *
 * @param $query
 *   The query string to split.
 *
 * @return
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 *   An array of URL decoded couples $param_name => $value.
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 */
function drupal_get_query_array($query) {
  $result = array();
  if (!empty($query)) {
    foreach (explode('&', $query) as $param) {
      $param = explode('=', $param);
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      $result[$param[0]] = isset($param[1]) ? rawurldecode($param[1]) : '';
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    }
  }
  return $result;
}

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/**
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 * Parses an array into a valid, rawurlencoded query string.
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 *
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 * @see \Drupal\Core\Routing\PathBasedGeneratorInterface::httpBuildQuery()
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 * @see drupal_get_query_parameters()
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 * @deprecated as of Drupal 8.0. Use
 *   Drupal::urlGenerator()->httpBuildQuery() instead.
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 * @ingroup php_wrappers
 */
function drupal_http_build_query(array $query, $parent = '') {
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  return Drupal::urlGenerator()->httpBuildQuery($query, $parent);
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}

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/**
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 * Prepares a 'destination' URL query parameter for use with url().
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 *
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 * 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.
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 *
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 * @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()
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 */
function drupal_get_destination() {
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  $destination = &drupal_static(__FUNCTION__);

  if (isset($destination)) {
    return $destination;
  }

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  if (isset($_GET['destination'])) {
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    $destination = array('destination' => $_GET['destination']);
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  }
  else {
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    $path = current_path();
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    $query = Drupal::urlGenerator()->httpBuildQuery(drupal_get_query_parameters());
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    if ($query != '') {
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      $path .= '?' . $query;
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    }
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    $destination = array('destination' => $path);
  }
  return $destination;
}

/**
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 * Parses a system URL string into an associative array suitable for url().
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 *
 * This function should only be used for URLs that have been generated by the
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 * system, such as via url(). It should not be used for URLs that come from
 * external sources, or URLs that link to external resources.
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 *
 * 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 $url, if existent.
 *
 * @see url()
 * @ingroup php_wrappers
 */
function drupal_parse_url($url) {
  $options = array(
    'path' => NULL,
    'query' => array(),
    'fragment' => '',
  );

  // External URLs: not using parse_url() here, so we do not have to rebuild
  // the scheme, host, and path without having any use for it.
  if (strpos($url, '://') !== FALSE) {
    // Split off everything before the query string into 'path'.
    $parts = explode('?', $url);
    $options['path'] = $parts[0];
    // If there is a query string, transform it into keyed query parameters.
    if (isset($parts[1])) {
      $query_parts = explode('#', $parts[1]);
      parse_str($query_parts[0], $options['query']);
      // Take over the fragment, if there is any.
      if (isset($query_parts[1])) {
        $options['fragment'] = $query_parts[1];
      }
    }
  }
  // Internal URLs.
  else {
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    // parse_url() does not support relative URLs, so make it absolute. E.g. the
    // relative URL "foo/bar:1" isn't properly parsed.
    $parts = parse_url('http://example.com/' . $url);
    // Strip the leading slash that was just added.
    $options['path'] = substr($parts['path'], 1);
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    if (isset($parts['query'])) {
      parse_str($parts['query'], $options['query']);
    }
    if (isset($parts['fragment'])) {
      $options['fragment'] = $parts['fragment'];
    }
  }

  return $options;
}

/**
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 * Encodes a Drupal path for use in a URL.
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 *
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 * For aesthetic reasons slashes are not escaped.
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 *
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 * Note that url() takes care of calling this function, so a path passed to that
 * function should not be encoded in advance.
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 *
 * @param $path
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 *   The Drupal path to encode.
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 */
function drupal_encode_path($path) {
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  return str_replace('%2F', '/', rawurlencode($path));
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}

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/**
 * Determines if an external URL points to this Drupal installation.
 *
 * @param $url
 *   A string containing an external URL, such as "http://example.com/foo".
 *
 * @return
 *   TRUE if the URL has the same domain and base path.
 */
function _external_url_is_local($url) {
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  $url_parts = parse_url($url);
  $base_host = parse_url($GLOBALS['base_url'], PHP_URL_HOST);
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  if (!isset($url_parts['path'])) {
    return ($url_parts['host'] == $base_host);
  }
  else {
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    // When comparing base paths, we need a trailing slash to make sure a
    // partial URL match isn't occuring. Since base_path() always returns with
    // a trailing slash, we don't need to add the trailing slash here.
    return ($url_parts['host'] == $base_host && stripos($url_parts['path'], base_path()) === 0);
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  }
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}

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/**
 * 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) {
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  $proxy_exceptions = settings()->get('proxy_exceptions', array('localhost', '127.0.0.1'));
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  return !in_array(strtolower($host), $proxy_exceptions, TRUE);
}

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/**
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 * @} End of "defgroup http_handling".
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 */
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/**
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 * @defgroup validation Input validation
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 * @{
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 * Functions to validate user input.
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 */

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/**
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 * Verifies the syntax of the given e-mail address.
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 *
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 * This uses the
 * @link http://php.net/manual/filter.filters.validate.php PHP e-mail validation filter. @endlink
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 *
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 * @param $mail
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 *   A string containing an e-mail address.
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 *
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 * @return
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 *   TRUE if the address is in a valid format.
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 */
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function valid_email_address($mail) {
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  return (bool)filter_var($mail, FILTER_VALIDATE_EMAIL);
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}

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/**
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 * Verifies the syntax of the given URL.
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 *
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 * This function should only be used on actual URLs. It should not be used for
 * Drupal menu paths, which can contain arbitrary characters.
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 * Valid values per RFC 3986.
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 * @param $url
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 *   The URL to verify.
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 * @param $absolute
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 *   Whether the URL is absolute (beginning with a scheme such as "http:").
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 *
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 * @return
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 *   TRUE if the URL is in a valid format.
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 *
 * @see \Drupal\Component\Utility\UrlValidator::isValid()
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 *
 * @deprecated as of Drupal 8.0. Use UrlValidator::isValid() instead.
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 */
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function valid_url($url, $absolute = FALSE) {
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  return UrlValidator::isValid($url, $absolute);
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}

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/**
 * 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);
}

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/**
 * @} End of "defgroup validation".
 */

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/**
 * @defgroup sanitization Sanitization functions
 * @{
 * Functions to sanitize values.
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 *
 * See http://drupal.org/writing-secure-code for information
 * on writing secure code.
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 */

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/**
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 * 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
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 * be a plain-text string for passing to t(), l(),
 * Drupal\Core\Template\Attribute, or another function that will call
 * check_plain() separately.
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 *
 * @param $uri
 *   A plain-text URI that might contain dangerous protocols.
 *
 * @return
 *   A plain-text URI stripped of dangerous protocols. As with all plain-text
 *   strings, this return value must not be output to an HTML page without
 *   check_plain() being called on it. However, it can be passed to functions
 *   expecting plain-text strings.
 *
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 * @see \Drupal\Component\Utility\Url::stripDangerousProtocols()
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 */
function drupal_strip_dangerous_protocols($uri) {
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  return UrlValidator::stripDangerousProtocols($uri);
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}

/**
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 * Strips dangerous protocols from a URI and encodes it for output to HTML.
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 *
 * @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
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 *   value within a $attributes array passed to Drupal\Core\Template\Attribute,
 *   because Drupal\Core\Template\Attribute expects those values to be
 *   plain-text strings. To pass a filtered URI to
 *   Drupal\Core\Template\Attribute, call drupal_strip_dangerous_protocols()
 *   instead.
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 *
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 * @see \Drupal\Component\Utility\Url::stripDangerousProtocols()
 * @see \Drupal\Component\Utility\String::checkPlain()
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 */
function check_url($uri) {
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  return String::checkPlain(UrlValidator::stripDangerousProtocols($uri));
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}

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/**
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 * Applies a very permissive XSS/HTML filter for admin-only use.
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 *
 * 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.
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 *
 * @param string $string
 *   The string to apply the filter to.
 *
 * @return string
 *   The filtered string.
 *
 * @see \Drupal\Component\Utility\Xss::filterAdmin()
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 */
function filter_xss_admin($string) {
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  return Xss::filterAdmin($string);
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}

/**
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 * Filters HTML to prevent cross-site-scripting (XSS) vulnerabilities.
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 *
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 * 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.
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 *
 * This code does four things:
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 * - 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:).
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 *
 * @param $string
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 *   The string with raw HTML in it. It will be stripped of everything that can
 *   cause an XSS attack.
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 * @param $allowed_tags
 *   An array of allowed tags.
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 *
 * @return
 *   An XSS safe version of $string, or an empty string if $string is not
 *   valid UTF-8.
 *
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 * @see \Drupal\Component\Utility\Xss::filter()
 *
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 * @ingroup sanitization
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 */
function filter_xss($string, $allowed_tags = array('a', 'em', 'strong', 'cite', 'blockquote', 'code', 'ul', 'ol', 'li', 'dl', 'dt', 'dd')) {
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  return Xss::filter($string, $allowed_tags);
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}

/**
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 * Processes an HTML attribute value and strips dangerous protocols from URLs.
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 *
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 * @param string $string
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 *   The string with the attribute value.
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 *
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 * @return string
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 *   Cleaned up and HTML-escaped version of $string.
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 *
 * @see \Drupal\Component\Utility\Url::filterBadProtocol()
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 */
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function filter_xss_bad_protocol($string) {
  return UrlValidator::filterBadProtocol($string);
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}

/**
 * @} End of "defgroup sanitization".
 */

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/**
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 * @defgroup format Formatting
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 * @{
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 * Functions to format numbers, strings, dates, etc.
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 */

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/**
 * Formats an RSS channel.
 *
 * Arbitrary elements may be added using the $args associative array.
 */
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function format_rss_channel($title, $link, $description, $items, $langcode = NULL, $args = array()) {
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  $langcode = $langcode ? $langcode : language(Language::TYPE_CONTENT)->langcode;
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  $output = "<channel>\n";
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  $output .= ' <title>' . check_plain($title) . "</title>\n";
  $output .= ' <link>' . check_url($link) . "</link>\n";
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  // 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;).
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  $output .= ' <description>' . check_plain(decode_entities(strip_tags($description))) . "</description>\n";
  $output .= ' <language>' . check_plain($langcode) . "</language>\n";
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  $output .= format_xml_elements($args);
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  $output .= $items;
  $output .= "</channel>\n";

  return $output;
}

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/**
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 * Formats a single RSS item.
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 *
 * Arbitrary elements may be added using the $args associative array.
 */
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function format_rss_item($title, $link, $description, $args = array()) {
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  $output = "<item>\n";
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  $output .= ' <title>' . check_plain($title) . "</title>\n";
  $output .= ' <link>' . check_url($link) . "</link>\n";
  $output .= ' <description>' . check_plain($description) . "</description>\n";
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  $output .= format_xml_elements($args);
  $output .= "</item>\n";

  return $output;
}

/**
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 * Formats XML elements.
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 *
 * @param $array
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 *   An array where each item represents an element and is either a:
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 *   - (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) {
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  $output = '';
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  foreach ($array as $key => $value) {
    if (is_numeric($key)) {
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      if ($value['key']) {
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        $output .= ' <' . $value['key'];
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        if (isset($value['attributes']) && is_array($value['attributes'])) {
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          $output .= new Attribute($value['attributes']);
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        }

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        if (isset($value['value']) && $value['value'] != '') {
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          $output .= '>' . (is_array($value['value']) ? format_xml_elements($value['value']) : check_plain($value['value'])) . '</' . $value['key'] . ">\n";
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        }
        else {
          $output .= " />\n";
        }
      }
    }
    else {
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      $output .= ' <' . $key . '>' . (is_array($value) ? format_xml_elements($value) : check_plain($value)) . "</$key>\n";
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    }
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  }
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  return $output;
}

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/**
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 * Formats a string containing a count of items.
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 *
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 * This function ensures that the string is pluralized correctly. Since t() is
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 * called by this function, make sure not to pass already-localized strings to
 * it.
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 *
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 * 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.',
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 *     array('%old-type' => $info->old_type, '%new-type' => $info->new_type));
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 * @endcode
 *
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 * @param $count
 *   The item count to display.
 * @param $singular
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 *   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.
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 * @param $plural
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 *   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".
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 * @param $args
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 *   An associative array of replacements to make after translation. Instances
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 *   of any key in this array are replaced with the corresponding value.
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 *   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.
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 * @param $options
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 *   An associative array of additional options. See t() for allowed keys.
 *
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 * @return
 *   A translated string.
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 *
 * @see t()
 * @see format_string()
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 */
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function format_plural($count, $singular, $plural, array $args = array(), array $options = array()) {
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  $args['@count'] = $count;
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