system.api.php 116 KB
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<?php
// $Id$

/**
 * @file
 * Hooks provided by Drupal core and the System module.
 */

/**
 * @addtogroup hooks
 * @{
 */

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/**
 * Defines one or more hooks that are exposed by a module.
 *
 * Normally hooks do not need to be explicitly defined. However, by declaring a
 * hook explicitly, a module may define a "group" for it. Modules that implement
 * a hook may then place their implementation in either $module.module or in
 * $module.$group.inc. If the hook is located in $module.$group.inc, then that
 * file will be automatically loaded when needed.
 * In general, hooks that are rarely invoked and/or are very large should be
 * placed in a separate include file, while hooks that are very short or very
 * frequently called should be left in the main module file so that they are
 * always available.
 *
 * @return
 *   An associative array whose keys are hook names and whose values are an
 *   associative array containing:
 *   - group: A string defining the group to which the hook belongs. The module
 *     system will determine whether a file with the name $module.$group.inc
 *     exists, and automatically load it when required.
 *
 * See system_hook_info() for all hook groups defined by Drupal core.
 */
function hook_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'tokens',
  );
  $hooks['tokens'] = array(
    'group' => 'tokens',
  );
  return $hooks;
}

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/**
 * Inform the base system and the Field API about one or more entity types.
 *
 * Inform the system about one or more entity types (i.e., object types that
 * can be loaded via entity_load() and, optionally, to which fields can be
 * attached).
 *
 * @see entity_load()
 * @see hook_entity_info_alter()
 *
 * @return
 *   An array whose keys are entity type names and whose values identify
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 *   properties of those types that the system needs to know about:
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 *   - label: The human-readable name of the type.
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 *   - controller class: The name of the class that is used to load the objects.
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 *     The class has to implement the DrupalEntityControllerInterface interface.
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 *     Leave blank to use the DrupalDefaultEntityController implementation.
 *   - base table: (used by DrupalDefaultEntityController) The name of the
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 *     entity type's base table.
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 *   - static cache: (used by DrupalDefaultEntityController) FALSE to disable
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 *     static caching of entities during a page request. Defaults to TRUE.
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 *   - load hook: The name of the hook which should be invoked by
 *     DrupalDefaultEntityController:attachLoad(), for example 'node_load'.
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 *   - path callback: A function taking an entity as argument and returning the
 *     path to the entity.
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 *   - fieldable: Set to TRUE if you want your entity type to be fieldable.
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 *   - object keys: An array describing how the Field API can extract the
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 *     information it needs from the objects of the type. Elements:
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 *     - id: The name of the property that contains the primary id of the
 *       object. Every object passed to the Field API must have this property
 *       and its value must be numeric.
 *     - revision: The name of the property that contains the revision id of
 *       the object. The Field API assumes that all revision ids are unique
 *       across all objects of a type.
 *       This element can be omitted if the objects of this type are not
 *       versionable.
 *     - bundle: The name of the property that contains the bundle name for the
 *       object. The bundle name defines which set of fields are attached to
 *       the object (e.g. what nodes call "content type").
 *       This element can be omitted if this type has no bundles (all objects
 *       have the same fields).
 *   - bundle keys: An array describing how the Field API can extract the
 *     information it needs from the bundle objects for this type (e.g
 *     $vocabulary objects for terms; not applicable for nodes).
 *     This element can be omitted if this type's bundles do not exist as
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 *     standalone objects. Elements:
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 *     - bundle: The name of the property that contains the name of the bundle
 *       object.
 *   - cacheable: A boolean indicating whether Field API should cache
 *     loaded fields for each object, reducing the cost of
 *     field_attach_load().
 *   - bundles: An array describing all bundles for this object type.
 *     Keys are bundles machine names, as found in the objects' 'bundle'
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 *     property (defined in the 'object keys' entry above). Elements:
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 *     - label: The human-readable name of the bundle.
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 *     - admin: An array of information that allows Field UI pages to attach 
 *       themselves to the existing administration pages for the bundle. 
 *       Elements:
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 *       - path: the path of the bundle's main administration page, as defined
 *         in hook_menu(). If the path includes a placeholder for the bundle,
 *         the 'bundle argument', 'bundle helper' and 'real path' keys below
 *         are required.
 *       - bundle argument: The position of the placeholder in 'path', if any.
 *       - real path: The actual path (no placeholder) of the bundle's main
 *         administration page. This will be used to generate links.
 *       - access callback: As in hook_menu(). 'user_access' will be assumed if
 *         no value is provided.
 *       - access arguments: As in hook_menu().
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 *   - view modes: An array describing the view modes for the entity type. View
 *     modes let entities be displayed differently depending on the context.
 *     For instance, a node can be displayed differently on its own page
 *     ('full' mode), on the home page or taxonomy listings ('teaser' mode), or
 *     in an RSS feed ('rss' mode). Modules taking part in the display of the
 *     entity (notably the Field API) can adjust their behavior depending on
 *     the requested view mode. Keys of the array are view mode names. Each
 *     view mode is described by an array with the following key/value pairs:
 *     - label: The human-readable name of the view mode
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 */
function hook_entity_info() {
  $return = array(
    'node' => array(
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      'label' => t('Node'),
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      'controller class' => 'NodeController',
      'base table' => 'node',
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      'revision table' => 'node_revision',
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      'path callback' => 'node_path',
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      'fieldable' => TRUE,
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      'object keys' => array(
        'id' => 'nid',
        'revision' => 'vid',
        'bundle' => 'type',
      ),
      'bundle keys' => array(
        'bundle' => 'type',
      ),
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      // Node.module handles its own caching.
      // 'cacheable' => FALSE,
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      'bundles' => array(),
      'view modes' => array(
        'full' => array(
          'label' => t('Full node'),
        ),
        'teaser' => array(
          'label' => t('Teaser'),
        ),
        'rss' => array(
          'label' => t('RSS'),
        ),
      ),
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    ),
  );
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  // Search integration is provided by node.module, so search-related
  // view modes for nodes are defined here and not in search.module.
  if (module_exists('search')) {
    $return['node']['view modes'] += array(
      'search_index' => array(
        'label' => t('Search index'),
      ),
      'search_result' => array(
        'label' => t('Search result'),
      ),
    );
  }

  // Bundles must provide a human readable name so we can create help and error
  // messages, and the path to attach Field admin pages to.
  foreach (node_type_get_names() as $type => $name) {
    $return['node']['bundles'][$type] = array(
      'label' => $name,
      'admin' => array(
        'path' => 'admin/structure/types/manage/%node_type',
        'real path' => 'admin/structure/types/manage/' . str_replace('_', '-', $type),
        'bundle argument' => 4,
        'access arguments' => array('administer content types'),
      ),
    );
  }

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  return $return;
}

/**
 * Alter the entity info.
 *
 * Modules may implement this hook to alter the information that defines an
 * entity. All properties that are available in hook_entity_info() can be
 * altered here.
 *
 * @see hook_entity_info()
 *
 * @param $entity_info
 *   The entity info array, keyed by entity name.
 */
function hook_entity_info_alter(&$entity_info) {
  // Set the controller class for nodes to an alternate implementation of the
  // DrupalEntityController interface.
  $entity_info['node']['controller class'] = 'MyCustomNodeController';
}

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/**
 * Act on entities when loaded.
 *
 * This is a generic load hook called for all entity types loaded via the
 * entity API.
 *
 * @param $entities
 *   The entities keyed by entity ID.
 * @param $type
 *   The type of entities being loaded (i.e. node, user, comment).
 */
function hook_entity_load($entities, $type) {
  foreach ($entities as $entity) {
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    $entity->foo = mymodule_add_something($entity, $type);
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  }
}

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/**
 * Define administrative paths.
 *
 * Modules may specify whether or not the paths they define in hook_menu() are
 * to be considered administrative. Other modules may use this information to
 * display those pages differently (e.g. in a modal overlay, or in a different
 * theme).
 *
 * To change the administrative status of menu items defined in another module's
 * hook_menu(), modules should implement hook_admin_paths_alter().
 *
 * @return
 *   An associative array. For each item, the key is the path in question, in
 *   a format acceptable to drupal_match_path(). The value for each item should
 *   be TRUE (for paths considered administrative) or FALSE (for non-
 *   administrative paths).
 *
 * @see hook_menu()
 * @see drupal_match_path()
 * @see hook_admin_paths_alter()
 */
function hook_admin_paths() {
  $paths = array(
    'mymodule/*/add' => TRUE,
    'mymodule/*/edit' => TRUE,
  );
  return $paths;
}

/**
 * Redefine administrative paths defined by other modules.
 *
 * @param $paths
 *   An associative array of administrative paths, as defined by implementations
 *   of hook_admin_paths().
 *
 * @see hook_admin_paths()
 */
function hook_admin_paths_alter(&$paths) {
  // Treat all user pages as administrative.
  $paths['user'] = TRUE;
  $paths['user/*'] = TRUE;
  // Treat the forum topic node form as a non-administrative page.
  $paths['node/add/forum'] = FALSE;
}

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/**
 * Act on entities as they are being prepared for view.
 *
 * Allows you to operate on multiple entities as they are being prepared for
 * view. Only use this if attaching the data during the entity_load() phase
 * is not appropriate, for example when attaching other 'entity' style objects.
 *
 * @param $entities
 *   The entities keyed by entity ID.
 * @param $type
 *   The type of entities being loaded (i.e. node, user, comment).
 */
function hook_entity_prepare_view($entities, $type) {
  // Load a specific node into the user object for later theming.
  if ($type == 'user') {
    $nodes = mymodule_get_user_nodes(array_keys($entities));
    foreach ($entities as $uid => $entity) {
      $entity->user_node = $nodes[$uid];
    }
  }
}

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/**
 * Perform periodic actions.
 *
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 * This hook will only be called if cron.php is run (e.g. by crontab).
 *
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 * Modules that require to schedule some commands to be executed at regular
 * intervals can implement hook_cron(). The engine will then call the hook
 * at the appropriate intervals defined by the administrator. This interface
 * is particularly handy to implement timers or to automate certain tasks.
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 * Database maintenance, recalculation of settings or parameters are good
 * candidates for cron tasks.
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 *
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 * Short-running or not resource intensive tasks can be executed directly.
 *
 * Long-running tasks should use the queue API. To do this, one or more queues
 * need to be defined via hook_cron_queue_info(). Items that need to be
 * processed are appended to the defined queue, instead of processing them
 * directly in hook_cron().
 * Examples of jobs that are good candidates for
 * hook_cron_queue_info() include automated mailing, retrieving remote data, and
 * intensive file tasks.
 *
 * @return
 *   None.
 *
 * @see hook_cron_queue_info()
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 */
function hook_cron() {
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  // Short-running operation example, not using a queue:
  // Delete all expired records since the last cron run.
  $expires = variable_get('mymodule_cron_last_run', REQUEST_TIME);
  db_delete('mymodule_table')
    ->condition('expires', $expires, '>=')
    ->execute();
  variable_set('mymodule_cron_last_run', REQUEST_TIME);
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  // Long-running operation example, leveraging a queue:
  // Fetch feeds from other sites.
  $result = db_query('SELECT * FROM {aggregator_feed} WHERE checked + refresh < :time AND refresh != :never', array(
    ':time' => REQUEST_TIME,
    ':never' => AGGREGATOR_CLEAR_NEVER,
  ));
  $queue = DrupalQueue::get('aggregator_feeds');
  foreach ($result as $feed) {
    $queue->createItem($feed);
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  }
}

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/**
 * Declare queues holding items that need to be run periodically.
 *
 * While there can be only one hook_cron() process running at the same time,
 * there can be any number of processes defined here running. Because of
 * this, long running tasks are much better suited for this API. Items queued
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 * in hook_cron() might be processed in the same cron run if there are not many
 * items in the queue, otherwise it might take several requests, which can be
 * run in parallel.
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 *
 * @return
 *   An associative array where the key is the queue name and the value is
 *   again an associative array. Possible keys are:
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 *   - 'worker callback': The name of the function to call. It will be called
 *     with one argument, the item created via DrupalQueue::createItem() in
 *     hook_cron().
 *   - 'time': (optional) How much time Drupal should spend on calling this
 *     worker in seconds. Defaults to 15.
 *
 * @see hook_cron()
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 */
function hook_cron_queue_info() {
  $queues['aggregator_feeds'] = array(
    'worker callback' => 'aggregator_refresh',
    'time' => 15,
  );
  return $queues;
}

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/**
 * Allows modules to declare their own Forms API element types and specify their
 * default values.
 *
 * This hook allows modules to declare their own form element types and to
 * specify their default values. The values returned by this hook will be
 * merged with the elements returned by hook_form() implementations and so
 * can return defaults for any Form APIs keys in addition to those explicitly
 * mentioned below.
 *
 * Each of the form element types defined by this hook is assumed to have
 * a matching theme function, e.g. theme_elementtype(), which should be
 * registered with hook_theme() as normal.
 *
 * Form more information about custom element types see the explanation at
 * http://drupal.org/node/169815.
 *
 * @return
 *  An associative array describing the element types being defined. The array
 *  contains a sub-array for each element type, with the machine-readable type
 *  name as the key. Each sub-array has a number of possible attributes:
 *  - "#input": boolean indicating whether or not this element carries a value
 *    (even if it's hidden).
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 *  - "#process": array of callback functions taking $element, $form_state,
 *    and $complete_form.
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 *  - "#after_build": array of callback functions taking $element and $form_state.
 *  - "#validate": array of callback functions taking $form and $form_state.
 *  - "#element_validate": array of callback functions taking $element and
 *    $form_state.
 *  - "#pre_render": array of callback functions taking $element and $form_state.
 *  - "#post_render": array of callback functions taking $element and $form_state.
 *  - "#submit": array of callback functions taking $form and $form_state.
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 *  - "#title_display": optional string indicating if and how #title should be
 *    displayed, see theme_form_element() and theme_form_element_label().
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 *
 * @see hook_element_info_alter()
 * @see system_element_info()
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 */
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function hook_element_info() {
  $types['filter_format'] = array(
    '#input' => TRUE,
  );
  return $types;
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}

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/**
 * Alter the element type information returned from modules.
 *
 * A module may implement this hook in order to alter the element type defaults
 * defined by a module.
 *
 * @param &$type
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 *   All element type defaults as collected by hook_element_info().
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 *
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 * @see hook_element_info()
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 */
function hook_element_info_alter(&$type) {
  // Decrease the default size of textfields.
  if (isset($type['textfield']['#size'])) {
    $type['textfield']['#size'] = 40;
  }
}

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/**
 * Perform cleanup tasks.
 *
 * This hook is run at the end of each page request. It is often used for
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 * page logging and specialized cleanup. This hook MUST NOT print anything.
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 *
 * Only use this hook if your code must run even for cached page views.
 * If you have code which must run once on all non cached pages, use
 * hook_init instead. Thats the usual case. If you implement this hook
 * and see an error like 'Call to undefined function', it is likely that
 * you are depending on the presence of a module which has not been loaded yet.
 * It is not loaded because Drupal is still in bootstrap mode.
 *
 * @param $destination
 *   If this hook is invoked as part of a drupal_goto() call, then this argument
 *   will be a fully-qualified URL that is the destination of the redirect.
 */
function hook_exit($destination = NULL) {
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  db_update('counter')
    ->expression('hits', 'hits + 1')
    ->condition('type', 1)
    ->execute();
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}

/**
 * Perform necessary alterations to the JavaScript before it is presented on
 * the page.
 *
 * @param $javascript
 *   An array of all JavaScript being presented on the page.
 * @see drupal_add_js()
 * @see drupal_get_js()
 * @see drupal_js_defaults()
 */
function hook_js_alter(&$javascript) {
  // Swap out jQuery to use an updated version of the library.
  $javascript['misc/jquery.js']['data'] = drupal_get_path('module', 'jquery_update') . '/jquery.js';
}

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/**
 * Registers JavaScript/CSS libraries associated with a module.
 *
 * Modules implementing this return an array of arrays. The key to each
 * sub-array is the machine readable name of the library. Each library may
 * contain the following items:
 *
 * - 'title': The human readable name of the library.
 * - 'website': The URL of the library's web site.
 * - 'version': A string specifying the version of the library; intentionally
 *   not a float because a version like "1.2.3" is not a valid float. Use PHP's
 *   version_compare() to compare different versions.
 * - 'js': An array of JavaScript elements; each element's key is used as $data
 *   argument, each element's value is used as $options array for
 *   drupal_add_js(). To add library-specific (not module-specific) JavaScript
 *   settings, the key may be skipped, the value must specify
 *   'type' => 'setting', and the actual settings must be contained in a 'data'
 *   element of the value.
 * - 'css': Like 'js', an array of CSS elements passed to drupal_add_css().
 * - 'dependencies': An array of libraries that are required for a library. Each
 *   element is an array containing the module and name of the registered
 *   library. Note that all dependencies for each dependent library will be
 *   added when this library is added.
 *
 * Registered information for a library should contain re-usable data only.
 * Module- or implementation-specific data and integration logic should be added
 * separately.
 *
 * @return
 *   An array defining libraries associated with a module.
 *
 * @see system_library()
 * @see drupal_add_library()
 * @see drupal_get_library()
 */
function hook_library() {
  // Library One.
  $libraries['library-1'] = array(
    'title' => 'Library One',
    'website' => 'http://example.com/library-1',
    'version' => '1.2',
    'js' => array(
      drupal_get_path('module', 'my_module') . '/library-1.js' => array(),
    ),
    'css' => array(
      drupal_get_path('module', 'my_module') . '/library-2.css' => array(
        'type' => 'file',
        'media' => 'screen',
      ),
    ),
  );
  // Library Two.
  $libraries['library-2'] = array(
    'title' => 'Library Two',
    'website' => 'http://example.com/library-2',
    'version' => '3.1-beta1',
    'js' => array(
      // JavaScript settings may use the 'data' key.
      array(
        'type' => 'setting',
        'data' => array('library2' => TRUE),
      ),
    ),
    'dependencies' => array(
      // Require jQuery UI core by System module.
      array('system' => 'ui'),
      // Require our other library.
      array('my_module', 'library-1'),
      // Require another library.
      array('other_module', 'library-3'),
    ),
  );
  return $libraries;
}

/**
 * Alters the JavaScript/CSS library registry.
 *
 * Allows certain, contributed modules to update libraries to newer versions
 * while ensuring backwards compatibility. In general, such manipulations should
 * only be done by designated modules, since most modules that integrate with a
 * certain library also depend on the API of a certain library version.
 *
 * @param $libraries
 *   The JavaScript/CSS libraries provided by $module. Keyed by internal library
 *   name and passed by reference.
 * @param $module
 *   The name of the module that registered the libraries.
 *
 * @see hook_library()
 */
function hook_library_alter(&$libraries, $module) {
  // Update Farbtastic to version 2.0.
  if ($module == 'system' && isset($libraries['farbtastic'])) {
    // Verify existing version is older than the one we are updating to.
    if (version_compare($libraries['farbtastic']['version'], '2.0', '<')) {
      // Update the existing Farbtastic to version 2.0.
      $libraries['farbtastic']['version'] = '2.0';
      $libraries['farbtastic']['js'] = array(
        drupal_get_path('module', 'farbtastic_update') . '/farbtastic-2.0.js' => array(),
      );
    }
  }
}

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/**
 * Alter CSS files before they are output on the page.
 *
 * @param $css
 *   An array of all CSS items (files and inline CSS) being requested on the page.
 * @see drupal_add_css()
 * @see drupal_get_css()
 */
function hook_css_alter(&$css) {
  // Remove defaults.css file.
  unset($css[drupal_get_path('module', 'system') . '/defaults.css']);
}

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/**
 * Add elements to a page before it is rendered.
 *
 * Use this hook when you want to add elements at the page level. For your
 * additions to be printed, they have to be placed below a top level array key
 * of the $page array that has the name of a region of the active theme.
 *
 * By default, valid region keys are 'page_top', 'header', 'sidebar_first',
 * 'content', 'sidebar_second' and 'page_bottom'. To get a list of all regions
 * of the active theme, use system_region_list($theme). Note that $theme is a
 * global variable.
 *
 * If you want to alter the elements added by other modules or if your module
 * depends on the elements of other modules, use hook_page_alter() instead which
 * runs after this hook.
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
 * @see hook_page_alter()
 * @see drupal_render_page()
 */
function hook_page_build(&$page) {
  if (menu_get_object('node', 1)) {
    // We are on a node detail page. Append a standard disclaimer to the
    // content region.
    $page['content']['disclaimer'] = array(
      '#markup' => t('Acme, Inc. is not responsible for the contents of this sample code.'),
      '#weight' => 25,
    );
  }
}

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/**
 * Perform alterations before a page is rendered.
 *
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 * Use this hook when you want to remove or alter elements at the page
 * level, or add elements at the page level that depend on an other module's
 * elements (this hook runs after hook_page_build().
 *
 * If you are making changes to entities such as forms, menus, or user
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 * profiles, use those objects' native alter hooks instead (hook_form_alter(),
 * for example).
 *
 * The $page array contains top level elements for each block region:
 * @code
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 *   $page['page_top']
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 *   $page['header']
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 *   $page['sidebar_first']
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 *   $page['content']
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 *   $page['sidebar_second']
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 *   $page['page_bottom']
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 * @endcode
 *
 * The 'content' element contains the main content of the current page, and its
 * structure will vary depending on what module is responsible for building the
 * page. Some legacy modules may not return structured content at all: their
 * pre-rendered markup will be located in $page['content']['main']['#markup'].
 *
 * Pages built by Drupal's core Node and Blog modules use a standard structure:
 *
 * @code
 *   // Node body.
 *   $page['content']['nodes'][$nid]['body']
 *   // Array of links attached to the node (add comments, read more).
 *   $page['content']['nodes'][$nid]['links']
 *   // The node object itself.
 *   $page['content']['nodes'][$nid]['#node']
 *   // The results pager.
 *   $page['content']['pager']
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 * @endcode
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 *
 * Blocks may be referenced by their module/delta pair within a region:
 * @code
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 *   // The login block in the first sidebar region.
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 *   $page['sidebar_first']['user_login']['#block'];
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 * @endcode
 *
 * @param $page
 *   Nested array of renderable elements that make up the page.
 *
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 * @see hook_page_build()
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 * @see drupal_render_page()
 */
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function hook_page_alter(&$page) {
  // Add help text to the user login block.
  $page['sidebar_first']['user_login']['help'] = array(
    '#weight' => -10,
    '#markup' => t('To post comments or add new content, you first have to log in.'),
  );
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}

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/**
 * Perform alterations before a form is rendered.
 *
 * One popular use of this hook is to add form elements to the node form. When
 * altering a node form, the node object retrieved at from $form['#node'].
 *
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 * Note that instead of hook_form_alter(), which is called for all forms, you
 * can also use hook_form_FORM_ID_alter() to alter a specific form.
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 *
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 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 * @param $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
 */
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function hook_form_alter(&$form, &$form_state, $form_id) {
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  if (isset($form['type']) && $form['type']['#value'] . '_node_settings' == $form_id) {
    $form['workflow']['upload_' . $form['type']['#value']] = array(
      '#type' => 'radios',
      '#title' => t('Attachments'),
      '#default_value' => variable_get('upload_' . $form['type']['#value'], 1),
      '#options' => array(t('Disabled'), t('Enabled')),
    );
  }
}

/**
 * Provide a form-specific alteration instead of the global hook_form_alter().
 *
 * Modules can implement hook_form_FORM_ID_alter() to modify a specific form,
 * rather than implementing hook_form_alter() and checking the form ID, or
 * using long switch statements to alter multiple forms.
 *
 * Note that this hook fires before hook_form_alter(). Therefore all
 * implementations of hook_form_FORM_ID_alter() will run before all implementations
 * of hook_form_alter(), regardless of the module order.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 *
 * @see drupal_prepare_form().
 */
function hook_form_FORM_ID_alter(&$form, &$form_state) {
  // Modification for the form with the given form ID goes here. For example, if
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  // FORM_ID is "user_register_form" this code would run only on the user
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  // registration form.

  // Add a checkbox to registration form about agreeing to terms of use.
  $form['terms_of_use'] = array(
    '#type' => 'checkbox',
    '#title' => t("I agree with the website's terms and conditions."),
    '#required' => TRUE,
  );
}

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/**
 * Allow themes to alter the theme-specific settings form.
 *
 * With this hook, themes can alter the theme-specific settings form in any way
 * allowable by Drupal's Forms API, such as adding form elements, changing
 * default values and removing form elements. See the Forms API documentation on
 * api.drupal.org for detailed information.
 *
 * Note that the base theme's form alterations will be run before any sub-theme
 * alterations.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 */
function hook_form_system_theme_settings_alter(&$form, &$form_state) {
  // Add a checkbox to toggle the breadcrumb trail.
  $form['toggle_breadcrumb'] = array(
    '#type' => 'checkbox',
    '#title' => t('Display the breadcrumb'),
    '#default_value' => theme_get_setting('toggle_breadcrumb'),
    '#description'   => t('Show a trail of links from the homepage to the current page.'),
  );
}

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/**
 * Map form_ids to builder functions.
 *
 * This hook allows modules to build multiple forms from a single form "factory"
 * function but each form will have a different form id for submission,
 * validation, theming or alteration by other modules.
 *
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 * The 'callback arguments' will be passed as parameters to the function defined
 * in 'callback'. In case the code that calls drupal_get_form() also passes
 * parameters, then the 'callback' function will receive the
 * 'callback arguments' specified in hook_forms() before those that have been
 * passed to drupal_get_form().
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 *
 * See node_forms() for an actual example of how multiple forms share a common
 * building function.
 *
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 * @param $form_id
 *   The unique string identifying the desired form.
 * @param $args
 *   An array containing the original arguments provided to drupal_get_form().
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 *   These are always passed to the form builder and do not have to be specified
 *   manually in 'callback arguments'.
 *
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 * @return
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 *   An associative array whose keys define form_ids and whose values are an
 *   associative array defining the following keys:
 *   - callback: The name of the form builder function to invoke.
 *   - callback arguments: (optional) Additional arguments to pass to the
 *     function defined in 'callback', which are prepended to $args.
 *   - wrapper_callback: (optional) The name of a form builder function to
 *     invoke before the form builder defined in 'callback' is invoked. This
 *     wrapper callback may prepopulate the $form array with form elements,
 *     which will then be already contained in the $form that is passed on to
 *     the form builder defined in 'callback'. For example, a wrapper callback
 *     could setup wizard-alike form buttons that are the same for a variety of
 *     forms that belong to the wizard, which all share the same wrapper
 *     callback.
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 */
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function hook_forms($form_id, $args) {
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  // Simply reroute the (non-existing) $form_id 'mymodule_first_form' to
  // 'mymodule_main_form'.
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  $forms['mymodule_first_form'] = array(
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    'callback' => 'mymodule_main_form',
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  );
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  // Reroute the $form_id and prepend an additional argument that gets passed to
  // the 'mymodule_main_form' form builder function.
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  $forms['mymodule_second_form'] = array(
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    'callback' => 'mymodule_main_form',
    'callback arguments' => array('some parameter'),
  );

  // Reroute the $form_id, but invoke the form builder function
  // 'mymodule_main_form_wrapper' first, so we can prepopulate the $form array
  // that is passed to the actual form builder 'mymodule_main_form'.
  $forms['mymodule_wrapped_form'] = array(
    'callback' => 'mymodule_main_form',
    'wrapper_callback' => 'mymodule_main_form_wrapper',
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  );
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  return $forms;
}

/**
 * Perform setup tasks. See also, hook_init.
 *
 * This hook is run at the beginning of the page request. It is typically
 * used to set up global parameters which are needed later in the request.
 *
 * Only use this hook if your code must run even for cached page views.This hook
 * is called before modules or most include files are loaded into memory.
 * It happens while Drupal is still in bootstrap mode.
 */
function hook_boot() {
  // we need user_access() in the shutdown function. make sure it gets loaded
  drupal_load('module', 'user');
  register_shutdown_function('devel_shutdown');
}

/**
 * Perform setup tasks. See also, hook_boot.
 *
 * This hook is run at the beginning of the page request. It is typically
 * used to set up global parameters which are needed later in the request.
 * when this hook is called, all modules are already loaded in memory.
 *
 * For example, this hook is a typical place for modules to add CSS or JS
 * that should be present on every page. This hook is not run on cached
 * pages - though CSS or JS added this way will be present on a cached page.
 */
function hook_init() {
  drupal_add_css(drupal_get_path('module', 'book') . '/book.css');
}

/**
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 * Define image toolkits provided by this module.
 *
 * The file which includes each toolkit's functions must be declared as part of
 * the files array in the module .info file so that the registry will find and
 * parse it.
 *
 * The toolkit's functions must be named image_toolkitname_operation().
 * where the operation may be:
 *   - 'load': Required. See image_gd_load() for usage.
 *   - 'save': Required. See image_gd_save() for usage.
 *   - 'settings': Optional. See image_gd_settings() for usage.
 *   - 'resize': Optional. See image_gd_resize() for usage.
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 *   - 'rotate': Optional. See image_gd_rotate() for usage.
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 *   - 'crop': Optional. See image_gd_crop() for usage.
 *   - 'desaturate': Optional. See image_gd_desaturate() for usage.
 *
 * @return
 *   An array with the toolkit name as keys and sub-arrays with these keys:
 *     - 'title': A string with the toolkit's title.
 *     - 'available': A Boolean value to indicate that the toolkit is operating
 *       properly, e.g. all required libraries exist.
 *
 * @see system_image_toolkits()
 */
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function hook_image_toolkits() {
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  return array(
    'working' => array(
      'title' => t('A toolkit that works.'),
      'available' => TRUE,
    ),
    'broken' => array(
      'title' => t('A toolkit that is "broken" and will not be listed.'),
      'available' => FALSE,
    ),
  );
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}

/**
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 * Alter an email message created with the drupal_mail() function.
 *
 * hook_mail_alter() allows modification of email messages created and sent
 * with drupal_mail(). Usage examples include adding and/or changing message
 * text, message fields, and message headers.
 *
 * Email messages sent using functions other than drupal_mail() will not
 * invoke hook_mail_alter(). For example, a contributed module directly
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 * calling the drupal_mail_system()->mail() or PHP mail() function
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 * will not invoke this hook. All core modules use drupal_mail() for
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 * messaging, it is best practice but not mandatory in contributed modules.
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 *
 * @param $message
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 *   An array containing the message data. Keys in this array include:
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 *  - 'id':
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 *     The drupal_mail() id of the message. Look at module source code or
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 *     drupal_mail() for possible id values.
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 *  - 'to':
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 *     The address or addresses the message will be sent to. The
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 *     formatting of this string must comply with RFC 2822.
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 *  - 'from':
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 *     The address the message will be marked as being from, which is
 *     either a custom address or the site-wide default email address.
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 *  - 'subject':
 *     Subject of the email to be sent. This must not contain any newline
 *     characters, or the email may not be sent properly.
 *  - 'body':
 *     An array of strings containing the message text. The message body is
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 *     created by concatenating the individual array strings into a single text
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 *     string using "\n\n" as a separator.
 *  - 'headers':
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 *     Associative array containing mail headers, such as From, Sender,
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 *     MIME-Version, Content-Type, etc.
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 *  - 'params':
 *     An array of optional parameters supplied by the caller of drupal_mail()
 *     that is used to build the message before hook_mail_alter() is invoked.
 *  - 'language':
 *     The language object used to build the message before hook_mail_alter()
 *     is invoked.
 *
 * @see drupal_mail()
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 */
function hook_mail_alter(&$message) {
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  if ($message['id'] == 'modulename_messagekey') {
    $message['body'][] = "--\nMail sent out from " . variable_get('sitename', t('Drupal'));
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  }
}

/**
 * Alter the information parsed from module and theme .info files
 *
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 * This hook is invoked in _system_rebuild_module_data() and in
 * _system_rebuild_theme_data(). A module may implement this hook in order to
 * add to or alter the data generated by reading the .info file with
 * drupal_parse_info_file().
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 *
 * @param &$info
 *   The .info file contents, passed by reference so that it can be altered.
 * @param $file
 *   Full information about the module or theme, including $file->name, and
 *   $file->filename
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 * @param $type
 *   Either 'module' or 'theme', depending on the type of .info file that was
 *   passed.
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 */
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function hook_system_info_alter(&$info, $file, $type) {
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  // Only fill this in if the .info file does not define a 'datestamp'.
  if (empty($info['datestamp'])) {
    $info['datestamp'] = filemtime($file->filename);
  }
}

/**
 * Define user permissions.
 *
 * This hook can supply permissions that the module defines, so that they
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 * can be selected on the user permissions page and used to grant or restrict
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 * access to actions the module performs.
 *
 * Permissions are checked using user_access().
 *
 * For a detailed usage example, see page_example.module.
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 *
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 * @return
 *   An array of which permission names are the keys and their corresponding
 *   values are descriptions of each permission.
 *   The permission names (keys of the array) must not be wrapped with
 *   the t() function, since the string extractor takes care of
 *   extracting permission names defined in the perm hook for
 *   translation. The permission descriptions (values of the array)
 *   should be wrapped in the t() function so they can be translated.
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 */
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function hook_permission() {
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  return array(
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    'administer my module' =>  array(
      'title' => t('Administer my module'),
      'description' => t('Perform administration tasks for my module.'),
    ),
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  );
}

/**
 * Register a module (or theme's) theme implementations.