system.api.php 153 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.
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 *
 * @see hook_hook_info_alter().
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 */
function hook_hook_info() {
  $hooks['token_info'] = array(
    'group' => 'tokens',
  );
  $hooks['tokens'] = array(
    'group' => 'tokens',
  );
  return $hooks;
}

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/**
 * Alter information from hook_hook_info().
 *
 * @param $hooks
 *   Information gathered by module_hook_info() from other modules'
 *   implementations of hook_hook_info(). Alter this array directly.
 *   See hook_hook_info() for information on what this may contain.
 */
function hook_hook_info_alter(&$hooks) {
  // Our module wants to completely override the core tokens, so make
  // sure the core token hooks are not found.
  $hooks['token_info']['group'] = 'mytokens';
  $hooks['tokens']['group'] = 'mytokens';
}

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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).
 *
 * @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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 *   - field cache: (used by Field API loading and saving of field data) FALSE
 *     to disable Field API's persistent cache of field data. Only recommended
 *     if a higher level persistent cache is available for the entity type.
 *     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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 *   - uri callback: A function taking an entity as argument and returning the
 *     uri elements of the entity, e.g. 'path' and 'options'. The actual entity
 *     uri can be constructed by passing these elements to url().
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 *   - fieldable: Set to TRUE if you want your entity type to be fieldable.
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 *   - translation: An associative array of modules registered as field
 *     translation handlers. Array keys are the module names, array values
 *     can be any data structure the module uses to provide field translation.
 *     Any empty value disallows the module to appear as a translation handler.
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 *   - entity 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
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 *       entity. Every entity object passed to the Field API must have this
 *       property and its value must be numeric.
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 *     - revision: The name of the property that contains the revision id of
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 *       the entity. The Field API assumes that all revision ids are unique
 *       across all entities of a type. This entry can be omitted if the
 *       entities of this type are not versionable.
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 *     - bundle: The name of the property that contains the bundle name for the
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 *       entity. The bundle name defines which set of fields are attached to
 *       the entity (e.g. what nodes call "content type"). This entry can be
 *       omitted if this entity type exposes a single bundle (all entities have
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 *       the same collection of fields). The name of this single bundle will be
 *       the same as the entity type.
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 *   - bundle keys: An array describing how the Field API can extract the
 *     information it needs from the bundle objects for this type (e.g
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 *     $vocabulary objects for terms; not applicable for nodes). This entry can
 *     be omitted if this type's bundles do not exist as standalone objects.
 *     Elements:
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 *     - bundle: The name of the property that contains the name of the bundle
 *       object.
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 *   - bundles: An array describing all bundles for this object type. Keys are
 *     bundles machine names, as found in the objects' 'bundle' property
 *     (defined in the 'entity keys' entry above). Elements:
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 *     - label: The human-readable name of the bundle.
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 *     - uri callback: Same as the 'uri callback' key documented above for the
 *       entity type, but for the bundle only. When determining the URI of an
 *       entity, if a 'uri callback' is defined for both the entity type and
 *       the bundle, the one for the bundle is used.
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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.
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 *       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
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 *     the requested view mode. An additional 'default' view mode is available
 *     for all entity types. This view mode is not intended for actual entity
 *     display, but holds default display settings. For each available view
 *     mode, administrators can configure whether it should use its own set of
 *     field display settings, or just replicate the settings of the 'default'
 *     view mode, thus reducing the amount of display configurations to keep
 *     track of. Keys of the array are view mode names. Each view mode is
 *     described by an array with the following key/value pairs:
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 *     - label: The human-readable name of the view mode
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 *     - custom settings: A boolean specifying whether the view mode should by
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 *       default use its own custom field display settings. If FALSE, entities
 *       displayed in this view mode will reuse the 'default' display settings
 *       by default (e.g. right after the module exposing the view mode is
 *       enabled), but administrators can later use the Field UI to apply custom
 *       display settings specific to the view mode.
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 *
 * @see entity_load()
 * @see hook_entity_info_alter()
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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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      'uri callback' => 'node_uri',
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      'fieldable' => TRUE,
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      'translation' => array(
        'locale' => TRUE,
      ),
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      'entity keys' => array(
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        'id' => 'nid',
        'revision' => 'vid',
        'bundle' => 'type',
      ),
      'bundle keys' => array(
        'bundle' => 'type',
      ),
      'bundles' => array(),
      'view modes' => array(
        'full' => array(
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          'label' => t('Full content'),
          'custom settings' => FALSE,
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        ),
        'teaser' => array(
          'label' => t('Teaser'),
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          'custom settings' => TRUE,
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        ),
        'rss' => array(
          'label' => t('RSS'),
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          'custom settings' => FALSE,
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        ),
      ),
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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'),
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        'custom settings' => FALSE,
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      ),
      'search_result' => array(
        'label' => t('Search result'),
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        'custom settings' => FALSE,
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      ),
    );
  }

  // 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.
 *
 * @param $entity_info
 *   The entity info array, keyed by entity name.
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 *
 * @see hook_entity_info()
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 */
function hook_entity_info_alter(&$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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/**
 * Act on entities when inserted.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being inserted (i.e. node, user, comment).
 */
function hook_entity_insert($entity, $type) {
}

/**
 * Act on entities when updated.
 *
 * @param $entity
 *   The entity object.
 * @param $type
 *   The type of entity being updated (i.e. node, user, comment).
 */
function hook_entity_update($entity, $type) {
}

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/**
 * Alter or execute an EntityFieldQuery.
 *
 * @param EntityFieldQuery $query
 *   An EntityFieldQuery. One of the most important properties to be changed is
 *   EntityFieldQuery::executeCallback. If this is set to an existing function,
 *   this function will get the query as its single argument and its result
 *   will be the returned as the result of EntityFieldQuery::execute(). This can
 *   be used to change the behavior of EntityFieldQuery entirely. For example,
 *   the default implementation can only deal with one field storage engine, but
 *   it is possible to write a module that can query across field storage
 *   engines. Also, the default implementation presumes entities are stored in
 *   SQL, but the execute callback could instead query any other entity storage,
 *   local or remote.
 */
function hook_entity_query_alter($query) {
  $query->executeCallback = 'my_module_query_callback';
}

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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 some commands to be executed periodically can
 * implement hook_cron(). The engine will then call the hook whenever a cron
 * run happens, as defined by the administrator. Typical tasks managed by
 * hook_cron() are database maintenance, backups, recalculation of settings
 * or parameters, automated mailing, and retrieving remote data.
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 *
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 * Short-running or non-resource-intensive tasks can be executed directly in
 * the hook_cron() implementation.
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 *
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 * Long-running tasks and tasks that could time out, such as retrieving remote
 * data, sending email, and intensive file tasks, should use the queue API
 * instead of executing the tasks directly. To do this, first define one or
 * more queues via hook_cron_queue_info(). Then, add items that need to be
 * processed to the defined queues.
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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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 * @see hook_cron_queue_info_alter()
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 */
function hook_cron_queue_info() {
  $queues['aggregator_feeds'] = array(
    'worker callback' => 'aggregator_refresh',
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    'time' => 60,
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  );
  return $queues;
}

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/**
 * Alter cron queue information before cron runs.
 *
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 * Called by drupal_cron_run() to allow modules to alter cron queue settings
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 * before any jobs are processesed.
 *
 * @param array $queues
 *   An array of cron queue information.
 *
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 * @see hook_cron_queue_info()
 * @see drupal_cron_run()
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 */
function hook_cron_queue_info_alter(&$queues) {
  // This site has many feeds so let's spend 90 seconds on each cron run
  // updating feeds instead of the default 60.
  $queues['aggregator_feeds']['time'] = 90;
}

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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 $javascript
 *   An array of all JavaScript being presented on the page.
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 *
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 * @see drupal_add_js()
 * @see drupal_get_js()
 * @see drupal_js_defaults()
 */
function hook_js_alter(&$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
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 *   element is an array listing the module and name of another library. Note
 *   that all dependencies for each dependent library will also be added when
 *   this library is added.
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 *
 * 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.
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      array('system', 'ui'),
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      // 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 $css
 *   An array of all CSS items (files and inline CSS) being requested on the page.
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 *
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 * @see drupal_add_css()
 * @see drupal_get_css()
 */
function hook_css_alter(&$css) {
  // Remove defaults.css file.
  unset($css[drupal_get_path('module', 'system') . '/defaults.css']);
}

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/**
 * Alter the commands that are sent to the user through the AJAX framework.
 *
 * @param $commands
 *   An array of all commands that will be sent to the user.
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 *
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 * @see ajax_render()
 */
function hook_ajax_render_alter($commands) {
  // Inject any new status messages into the content area.
  $commands[] = ajax_command_prepend('#block-system-main .content', theme('status_messages'));
}

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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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/**
 * Define menu items and page callbacks.
 *
 * This hook enables modules to register paths in order to define how URL
 * requests are handled. Paths may be registered for URL handling only, or they
 * can register a link to be placed in a menu (usually the Navigation menu). A
 * path and its associated information is commonly called a "menu router item".
 * This hook is rarely called (for example, when modules are enabled), and
 * its results are cached in the database.
 *
 * hook_menu() implementations return an associative array whose keys define
 * paths and whose values are an associative array of properties for each
 * path. (The complete list of properties is in the return value section below.)
 *
 * The definition for each path may include a page callback function, which is
 * invoked when the registered path is requested. If there is no other
 * registered path that fits the requested path better, any further path
 * components are passed to the callback function. For example, your module
 * could register path 'abc/def':
 * @code
 *   function mymodule_menu() {
 *     $items['abc/def'] = array(
 *       'page callback' => 'mymodule_abc_view',
 *     );
 *   }
 *
 *   function mymodule_abc_view($ghi = 0, $jkl = '') {
 *     // ...
 *   }
 * @endcode
 * When path 'abc/def' is requested, no further path components are in the
 * request, and no additional arguments are passed to the callback function (so
 * $ghi and $jkl would take the default values as defined in the function
 * signature). When 'abc/def/123/foo' is requested, $ghi will be '123' and
 * $jkl will be 'foo'. Note that this automatic passing of optional path
 * arguments applies only to page and theme callback functions.
 *
 * In addition to optional path arguments, the page callback and other callback
 * functions may specify argument lists as arrays. These argument lists may
 * contain both fixed/hard-coded argument values and integers that correspond
 * to path components. When integers are used and the callback function is
 * called, the corresponding path components will be substituted for the
 * integers. That is, the integer 0 in an argument list will be replaced with
 * the first path component, integer 1 with the second, and so on (path
 * components are numbered starting from zero). This substitution feature allows
 * you to re-use a callback function for several different paths. For example:
 * @code
 *   function mymodule_menu() {
 *     $items['abc/def'] = array(
 *       'page callback' => 'mymodule_abc_view',
 *       'page arguments' => array(1, 'foo'),
 *     );
 *   }
 * @endcode
 * When path 'abc/def' is requested, the page callback function will get 'def'
 * as the first argument and (always) 'foo' as the second argument.
 *
 * Note that if a page or theme callback function has an argument list array,
 * these arguments will be passed first to the function, followed by any
 * any arguments generated by optional path arguments as described above.
 *
 * Special care should be taken for the page callback drupal_get_form(), because
 * your specific form callback function will always receive $form and
 * &$form_state as the first function arguments:
 * @code
 *   function mymodule_abc_form($form, &$form_state) {
 *     // ...
 *     return $form;
 *   }
 * @endcode
 * See @link form_api Form API documentation @endlink for details.
 *
 * Wildcards within paths also work with integer substitution. For example,
 * your module could register path 'my-module/%/edit':
 * @code
 *   $items['my-module/%/edit'] = array(
 *     'page callback' => 'mymodule_abc_edit',
 *     'page arguments' => array(1),
 *   );
 * @endcode
 * When path 'my-module/foo/edit' is requested, integer 1 will be replaced
 * with 'foo' and passed to the callback function.
 *
 * Registered paths may also contain special "auto-loader" wildcard components
 * in the form of '%mymodule_abc', where the '%' part means that this path
 * component is a wildcard, and the 'mymodule_abc' part defines the prefix for a
 * load function, which here would be named mymodule_abc_load(). When a matching
 * path is requested, your load function will receive as its first argument the
 * path component in the position of the wildcard; load functions may also be
 * passed additional arguments (see "load arguments" in the return value
 * section below). For example, your module could register path
 * 'my-module/%mymodule_abc/edit':
 * @code
 *   $items['my-module/%mymodule_abc/edit'] = array(
 *     'page callback' => 'mymodule_abc_edit',
 *     'page arguments' => array(1),
 *   );
 * @endcode
 * When path 'my-module/123/edit' is requested, your load function
 * mymodule_abc_load() will be invoked with the argument '123', and should
 * load and return an "abc" object with internal id 123:
 * @code
 *   function mymodule_abc_load($abc_id) {
 *     return db_query("SELECT * FROM {mymodule_abc} WHERE abc_id = :abc_id", array(':abc_id' => $abc_id))->fetchObject();
 *   }
 * @endcode
 * This 'abc' object will then be passed into the page callback function
 * mymodule_abc_edit() to replace the integer 1 in the page arguments.
 *
 * You can also make groups of menu items to be rendered (by default) as tabs
 * on a page. To do that, first create one menu item of type MENU_NORMAL_ITEM,
 * with your chosen path, such as 'foo'. Then duplicate that menu item, using a
 * subdirectory path, such as 'foo/tab1', and changing the type to
 * MENU_DEFAULT_LOCAL_TASK to make it the default tab for the group. Then add
 * the additional tab items, with paths such as "foo/tab2" etc., with type
 * MENU_LOCAL_TASK. Example:
 * @code
 * // Make "Foo settings" appear on the admin Config page
 * $items['admin/config/foo'] = array(
 *   'title' => 'Foo settings',
 *   'type' => MENU_NORMAL_ITEM,
 *   // page callback, etc. need to be added here
 * );
 * // Make "Global settings" the main tab on the "Foo settings" page
 * $items['admin/config/foo/global'] = array(
 *   'title' => 'Global settings',
 *   'type' => MENU_DEFAULT_LOCAL_TASK,
 *   // access callback, page callback, and theme callback will be inherited
 *   // from 'admin/config/foo', if not specified here to override
 * );
 * // Make an additional tab called "Node settings" on "Foo settings"
 * $items['admin/config/foo/node'] = array(
 *   'title' => 'Node settings',
 *   'type' => MENU_LOCAL_TASK,
 *   // access callback, page callback, and theme callback will be inherited
 *   // from 'admin/config/foo', if not specified here to override
 * );
 * @endcode
 *
 * @return
 *   An array of menu items. Each menu item has a key corresponding to the
 *   Drupal path being registered. The corresponding array value is an
 *   associative array that may contain the following key-value pairs:
 *   - "title": Required. The untranslated title of the menu item.
 *   - "title callback": Function to generate the title; defaults to t().
 *     If you require only the raw string to be output, set this to FALSE.
 *   - "title arguments": Arguments to send to t() or your custom callback,
 *     with path component substitution as described above.
 *   - "description": The untranslated description of the menu item.
 *   - "page callback": The function to call to display a web page when the user
 *     visits the path. If omitted, the parent menu item's callback will be used
 *     instead.
 *   - "page arguments": An array of arguments to pass to the page callback
 *     function, with path component substitution as described above.
 *   - "delivery callback": The function to call to package the result of the
 *     page callback function and send it to the browser. Defaults to
 *     drupal_deliver_html_page() unless a value is inherited from a parent menu
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 *     item. Note that this function is called even if the access checks fail,
 *     so any custom delivery callback function should take that into account.
 *     See drupal_deliver_html_page() for an example.
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 *   - "access callback": A function returning a boolean value that determines
 *     whether the user has access rights to this menu item. Defaults to
 *     user_access() unless a value is inherited from a parent menu item.
 *   - "access arguments": An array of arguments to pass to the access callback
 *     function, with path component substitution as described above.
 *   - "theme callback": Optional. A function returning the machine-readable
 *     name of the default theme that will be used to render the page. If this
 *     function is provided, it is expected to return a currently-active theme
 *     on the site (otherwise, the main site theme will be used instead). If no
 *     function is provided, the main site theme will also be used, unless a
 *     value is inherited from a parent menu item. In all cases, the results of
 *     this function can be dynamically overridden for a particular page
 *     request by modules which implement hook_custom_theme().
 *   - "theme arguments": An array of arguments to pass to the theme callback
 *     function, with path component substitution as described above.
 *   - "file": A file that will be included before the page callback is called;
 *     this allows page callback functions to be in separate files. The file
 *     should be relative to the implementing module's directory unless
 *     otherwise specified by the "file path" option. Does not apply to other
 *     callbacks (only page callback).
 *   - "file path": The path to the directory containing the file specified in
 *     "file". This defaults to the path to the module implementing the hook.
 *   - "load arguments": An array of arguments to be passed to each of the
 *     wildcard object loaders in the path, after the path argument itself.
 *     For example, if a module registers path node/%node/revisions/%/view
 *     with load arguments set to array(3), the '%node' in the path indicates
 *     that the loader function node_load() will be called with the second
 *     path component as the first argument. The 3 in the load arguments
 *     indicates that the fourth path component will also be passed to
 *     node_load() (numbering of path components starts at zero). So, if path
 *     node/12/revisions/29/view is requested, node_load(12, 29) will be called.
 *     There are also two "magic" values that can be used in load arguments.
 *     "%index" indicates the index of the wildcard path component. "%map"
 *     indicates the path components as an array. For example, if a module
 *     registers for several paths of the form 'user/%user_category/edit/*', all
 *     of them can use the same load function user_category_load(), by setting
 *     the load arguments to array('%map', '%index'). For instance, if the user
 *     is editing category 'foo' by requesting path 'user/32/edit/foo', the load
 *     function user_category_load() will be called with 32 as its first
 *     argument, the array ('user', 32, 'edit', 'foo') as the map argument,
 *     and 1 as the index argument (because %user_category is the second path
 *     component and numbering starts at zero). user_category_load() can then
 *     use these values to extract the information that 'foo' is the category
 *     being requested.
 *   - "weight": An integer that determines the relative position of items in
 *     the menu; higher-weighted items sink. Defaults to 0. Menu items with the
 *     same weight are ordered alphabetically.
 *   - "menu_name": Optional. Set this to a custom menu if you don't want your
 *     item to be placed in Navigation.
 *   - "context": (optional) Defines the context a tab may appear in. By
 *     default, all tabs are only displayed as local tasks when being rendered
 *     in a page context. All tabs that should be accessible as contextual links
 *     in page region containers outside of the parent menu item's primary page
 *     context should be registered using one of the following contexts:
 *     - MENU_CONTEXT_PAGE: (default) The tab is displayed as local task for the
 *       page context only.
 *     - MENU_CONTEXT_INLINE: The tab is displayed as contextual link outside of
 *       the primary page context only.
 *     Contexts can be combined. For example, to display a tab both on a page
 *     and inline, a menu router item may specify:
 *     @code
 *       'context' => MENU_CONTEXT_PAGE | MENU_CONTEXT_INLINE,
 *     @endcode
 *   - "tab_parent": For local task menu items, the path of the task's parent
 *     item; defaults to the same path without the last component (e.g., the
 *     default parent for 'admin/people/create' is 'admin/people').
 *   - "tab_root": For local task menu items, the path of the closest non-tab
 *     item; same default as "tab_parent".
 *   - "block callback": Name of a function used to render the block on the
 *     system administration page for this item (called with no arguments).
 *     If not provided, system_admin_menu_block() is used to generate it.
 *   - "position": Position of the block ('left' or 'right') on the system
 *     administration page for this item.
 *   - "type": A bitmask of flags describing properties of the menu item.
 *     Many shortcut bitmasks are provided as constants in menu.inc:
 *     - MENU_NORMAL_ITEM: Normal menu items show up in the menu tree and can be
 *       moved/hidden by the administrator.
 *     - MENU_CALLBACK: Callbacks simply register a path so that the correct
 *       information is generated when the path is accessed.
 *     - MENU_SUGGESTED_ITEM: Modules may "suggest" menu items that the
 *       administrator may enable.
 *     - MENU_LOCAL_ACTION: Local actions are menu items that describe actions
 *       on the parent item such as adding a new user or block, and are
 *       rendered in the action-links list in your theme.
 *     - MENU_LOCAL_TASK: Local tasks are menu items that describe different
 *       displays of data, and are generally rendered as tabs.
 *     - MENU_DEFAULT_LOCAL_TASK: Every set of local tasks should provide one
 *       "default" task, which should display the same page as the parent item.
 *     If the "type" element is omitted, MENU_NORMAL_ITEM is assumed.
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 *   - "options": An array of options to be passed to l() when generating a link
 *     from this menu item.
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 *
 * For a detailed usage example, see page_example.module.
 * For comprehensive documentation on the menu system, see
 * http://drupal.org/node/102338.
 */
function hook_menu() {
  $items['blog'] = array(
    'title' => 'blogs',
    'page callback' => 'blog_page',
    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
  );
  $items['blog/feed'] = array(
    'title' => 'RSS feed',
    'page callback' => 'blog_feed',
    'access arguments' => array('access content'),
    'type' => MENU_CALLBACK,
  );

  return $items;
}

/**
 * Alter the data being saved to the {menu_router} table after hook_menu is invoked.
 *
 * This hook is invoked by menu_router_build(). The menu definitions are passed
 * in by reference. Each element of the $items array is one item returned
 * by a module from hook_menu. Additional items may be added, or existing items
 * altered.
 *
 * @param $items
 *   Associative array of menu router definitions returned from hook_menu().
 */
function hook_menu_alter(&$items) {
  // Example - disable the page at node/add
  $items['node/add']['access callback'] = FALSE;
}

/**
 * Alter the data being saved to the {menu_links} table by menu_link_save().
 *
 * @param $item
 *   Associative array defining a menu link as passed into menu_link_save().
 */
function hook_menu_link_alter(&$item) {
  // Example 1 - make all new admin links hidden (a.k.a disabled).
  if (strpos($item['link_path'], 'admin') === 0 && empty($item['mlid'])) {
    $item['hidden'] = 1;
  }
  // Example 2  - flag a link to be altered by hook_translated_menu_link_alter()
  if ($item['link_path'] == 'devel/cache/clear') {
    $item['options']['alter'] = TRUE;
  }
}

/**
 * Alter a menu link after it's translated, but before it's rendered.
 *
 * This hook may be used, for example, to add a page-specific query string.
 * For performance reasons, only links that have $item['options']['alter'] == TRUE
 * will be passed into this hook. The $item['options']['alter'] flag should
 * generally be set using hook_menu_link_alter().
 *
 * @param $item
 *   Associative array defining a menu link after _menu_link_translate()
 * @param $map
 *   Associative array containing the menu $map (path parts and/or objects).
 */
function hook_translated_menu_link_alter(&$item, $map) {
  if ($item['href'] == 'devel/cache/clear') {
    $item['localized_options']['query'] = drupal_get_destination();
  }
}

/**
 * Inform modules that a menu link has been created.
 *
 * This hook is used to notify modules that menu items have been
 * created. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_update()
 * @see hook_menu_link_delete()
 */
function hook_menu_link_insert($link) {
  // In our sample case, we track menu items as editing sections
  // of the site. These are stored in our table as 'disabled' items.
  $record['mlid'] = $link['mlid'];
  $record['menu_name'] = $link['menu_name'];
  $record['status'] = 0;
  drupal_write_record('menu_example', $record);
}

/**
 * Inform modules that a menu link has been updated.
 *
 * This hook is used to notify modules that menu items have been
 * updated. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_insert()
 * @see hook_menu_link_delete()
 */
function hook_menu_link_update($link) {
  // If the parent menu has changed, update our record.
  $menu_name = db_result(db_query("SELECT mlid, menu_name, status FROM {menu_example} WHERE mlid = :mlid", array(':mlid' => $link['mlid'])));
  if ($menu_name != $link['menu_name']) {
    db_update('menu_example')
      ->fields(array('menu_name' => $link['menu_name']))
      ->condition('mlid', $link['mlid'])
      ->execute();
  }
}

/**
 * Inform modules that a menu link has been deleted.
 *
 * This hook is used to notify modules that menu items have been
 * deleted. Contributed modules may use the information to perform
 * actions based on the information entered into the menu system.
 *
 * @param $link
 *   Associative array defining a menu link as passed into menu_link_save().
 *
 * @see hook_menu_link_insert()
 * @see hook_menu_link_update()
 */
function hook_menu_link_delete($link) {
  // Delete the record from our table.
  db_delete('menu_example')
    ->condition('mlid', $link['mlid'])
    ->execute();
}

/**
 * Alter tabs and actions displayed on the page before they are rendered.
 *
 * This hook is invoked by menu_local_tasks(). The system-determined tabs and
 * actions are passed in by reference. Additional tabs or actions may be added,
 * or existing items altered.
 *
 * Each tab or action is an associative array containing:
 * - #theme: The theme function to use to render.
 * - #link: An associative array containing:
 *   - title: The localized title of the link.
 *   - href: The system path to link to.
 *   - localized_options: An array of options to pass to url().
 * - #active: Whether the link should be marked as 'active'.
 *
 * @param $data
 *   An associative array containing:
 *   - actions: An associative array containing:
 *     - count: The amount of actions determined by the menu system, which can
 *       be ignored.
 *     - output: A list of of actions, each one being an associative array
 *       as described above.
 *   - tabs: An indexed array (list) of tab levels (up to 2 levels), each
 *     containing an associative array:
 *     - count: The amount of tabs determined by the menu system. This value
 *       does not need to be altered if there is more than one tab.
 *     - output: A list of of tabs, each one being an associative array as
 *       described above.
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 * @param $router_item
 *   The menu system router item of the page.
 * @param $root_path
 *   The path to the root item for this set of tabs.
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 */
function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
  // Add an action linking to node/add to all pages.
  $data['actions']['output'][] = array(
    '#theme' => 'menu_local_task',
    '#link' => array(
      'title' => t('Add new content'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add new content'),
        ),
      ),
    ),
  );

  // Add a tab linking to node/add to all pages.
  $data['tabs'][0]['output'][] = array(
    '#theme' => 'menu_local_task',
    '#link' => array(
      'title' => t('Example tab'),
      'href' => 'node/add',
      'localized_options' => array(
        'attributes' => array(
          'title' => t('Add new content'),
        ),
      ),
    ),
    // Define whether this link is active. This can be omitted for
    // implementations that add links to pages outside of the current page
    // context.
    '#active' => ($router_item['path'] == $root_path),
  );
}

/**
 * Alter contextual links before they are rendered.
 *
 * This hook is invoked by menu_contextual_links(). The system-determined
 * contextual links are passed in by reference. Additional links may be added
 * or existing links can be altered.
 *
 * Each contextual link must at least contain:
 * - title: The localized title of the link.
 * - href: The system path to link to.
 * - localized_options: An array of options to pass to url().
 *
 * @param $links
 *   An associative array containing contextual links for the given $root_path,
 *   as described above. The array keys are used to build CSS class names for
 *   contextual links and must therefore be unique for each set of contextual
 *   links.
 * @param $router_item
 *   The menu router item belonging to the $root_path being requested.
 * @param $root_path
 *   The (parent) path that has been requested to build contextual links for.
 *   This is a normalized path, which means that an originally passed path of
 *   'node/123' became 'node/%'.
 *
 * @see menu_contextual_links()
 * @see hook_menu()
 * @see system_preprocess()
 */
function hook_menu_contextual_links_alter(&$links, $router_item, $root_path) {
  // Add a link to all contextual links for nodes.
  if ($root_path == 'node/%') {
    $links['foo'] = array(
      'title' => t('Do fu'),
      'href' => 'foo/do',
      'localized_options' => array(
        'query' => array(
          'foo' => 'bar',
        ),
      ),
    );
  }
}

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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
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 * altering a node form, the node object can be accessed at $form['#node'].
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 *
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 * Note that instead of hook_form_alter(), which is called for all forms, you
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 * can also use hook_form_FORM_ID_alter() to alter a specific form. For each
 * module (in system weight order) the general form alter hook implementation
 * is invoked first, then the form ID specific alter implementation is called.
 * After all module hook implementations are invoked, the hook_form_alter()
 * implementations from themes are invoked in the same manner.
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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 $form_id
 *   String representing the name of the form itself. Typically this is the
 *   name of the function that generated the form.
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 *
 * @see hook_form_FORM_ID_alter()
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 */
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function hook_form_alter(&$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.
 *
 * @param $form
 *   Nested array of form elements that comprise the form.
 * @param $form_state
 *   A keyed array containing the current state of the form.
 *
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 * @see hook_form_alter()
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 * @see drupal_prepare_form()
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 */
function hook_form_FORM_ID_alter(&$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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 * Map form_ids to form builder functions.
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 *
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 * By default, when drupal_get_form() is called, the system will look for a
 * function with the same name as the form ID, and use that function to build
 * the form. This hook allows you to override that behavior in two ways.
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 *
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 * First, you can use this hook to tell the form system to use a different
 * function to build certain forms in your module; this is often used to define
 * a form "factory" function that is used to build several similar forms. In
 * this case, your hook implementation will likely ignore all of the input
 * arguments. See node_forms() for an example of this.
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 *
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 * Second, you could use this hook to define how to build a form with a
 * dynamically-generated form ID. In this case, you would need to verify that
 * the $form_id input matched your module's format for dynamically-generated
 * form IDs, and if so, act appropriately.
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 *
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 * @param $form_id
 *   The unique string identifying the desired form.
 * @param $args
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 *   An array containing the original arguments provided to drupal_get_form()
 *   or drupal_form_submit(). These are always passed to the form builder and
 *   do not have to be specified manually in 'callback arguments'.
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 *
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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');
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  drupal_register_shutdown_function('devel_shutdown');
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}

/**
 * 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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  }
}

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/**
 * Alter the registry of modules implementing a hook.
 *
 * This hook is invoked during module_implements(). A module may implement this
 * hook in order to reorder the implementing modules, which are otherwise
 * ordered by the module's system weight.
 *
 * @param &$implementations
 *   An array keyed by the module's name. The value of each item corresponds
 *   to a $group, which is usually FALSE, unless the implementation is in a
 *   file named $module.$group.inc.
 * @param $hook
 *   The name of the module hook being implemented.
 */
function hook_module_implements_alter(&$implementations, $hook) {
  if ($hook == 'rdf_mapping') {
    // Move my_module_rdf_mapping() to the end of the list. module_implements()
    // iterates through $implementations with a foreach loop which PHP iterates
    // in the order that the items were added, so to move an item to the end of
    // the array, we remove it and then add it.
    $group = $implementations['my_module'];
    unset($implementations['my_module']);
    $implementations['my_module'] = $group;
  }
}

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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
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 *   An array whose keys are permission names and whose corresponding values
 *   are arrays containing the following key-value pairs:
 *   - title: The human-readable name of the permission, to be shown on the
 *     permission administration page. This should be wrapped in the t()
 *     function so it can be translated.
 *   - description: (optional) A description of what the permission does. This
 *     should be wrapped in the t() function so it can be translated.
 *   - restrict access: (optional) A boolean which can be set to TRUE to
 *     indicate that site administrators should restrict access to this
 *     permission to trusted users. This should be used for permissions that
 *     have inherent security risks across a variety of potential use cases
 *     (for example, the "administer filters" and "bypass node access"
 *     permissions provided by Drupal core). When set to TRUE, a standard
 *     warning message defined in user_admin_permissions() will be associated
 *     with the permission and displayed with it on the permission
 *     administration page. Defaults to FALSE.
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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.
 *
 * The following parameters are all optional.
 *
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 * @param array $existing
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 *   An array of existing implementations that may be used for override
 *   purposes. This is primarily useful for themes that may wish to examine
 *   existing implementations to extract data (such as arguments) so that
 *   it may properly register its own, higher priority implementations.
 * @param $type
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 *   Whether a theme, module, etc. is being processed. This is primarily useful
 *   so that themes tell if they are the actual theme being called or a parent
 *   theme. May be one of:
 *   - 'module': A module is being checked for theme implementations.
 *   - 'base_theme_engine': A theme engine is being checked for a theme that is
 *     a parent of the actual theme being used.
 *   - 'theme_engine': A theme engine is being checked for the actual theme
 *     being used.
 *   - 'base_theme': A base theme is being checked for theme implementations.
 *   - 'theme': The actual theme in use is being checked.
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 * @param $theme
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 *   The actual name of theme, module, etc. that is being being processed.
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 * @param $path
 *   The directory path of the theme or module, so that it doesn't need to be
 *   looked up.
 *
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 * @return array
 *   An associative array of theme hook information. The keys on the outer
 *   array are the internal names of the hooks, and the values are arrays
 *   containing information about the hook. Each array may contain the
 *   following elements:
 *   - variables: (required if "render element" not present) An array of
 *     variables that this theme hook uses. This value allows the theme layer to
 *     properly utilize templates. Each array key represents the name of the
 *     variable and the value will be used as the default value if it is not
 *     given when theme() is called. Template implementations receive these
 *     arguments as variables in the template file. Function implementations
 *     are passed this array data in the $variables parameter.
 *   - render element: (required if "variables" not present) A string that is
 *     the name of the sole renderable element to pass to the theme function.
 *     The string represents the name of the "variable" that will hold the
 *     renderable array inside any optional preprocess or process functions.
 *     Cannot be used with the "variables" item; only one or the other, not
 *     both, can be present in a hook's info array.
 *   - file: The file the implementation resides in. This file will be included
 *     prior to the theme being rendered, to make sure that the function or
 *     preprocess function (as needed) is actually loaded; this makes it
 *     possible to split theme functions out into separate files quite easily.
 *   - path: Override the path of the file to be used. Ordinarily the module or
 *     theme path will be used, but if the file will not be in the default path,
 *     include it here. This path should be relative to the Drupal root
 *     directory.
 *   - template: If specified, this theme implementation is a template, and this
 *     is the template file without an extension. Do not put .tpl.php on this
 *     file; that extension will be added automatically by the default rendering
 *     engine (which is PHPTemplate). If 'path', above, is specified, the
 *     template should also be in this path.
 *   - function: If specified, this will be the function name to invoke for this
 *     implementation. If neither file nor function is specified, a default
 *     function name will be assumed. For example, if a module registers
 *     the 'node' theme hook, 'theme_node' will be assigned to its function.
 *     If the chameleon theme registers the node hook, it will be assigned
 *     'chameleon_node' as its function.
 *   - pattern: A regular expression pattern to be used to allow this theme
 *     implementation to have a dynamic name. The convention is to use __ to
 *     differentiate the dynamic portion of the theme. For example, to allow
 *     forums to be themed individually, the pattern might be: 'forum__'. Then,
 *     when the forum is themed, call:
 *     @code
 *     theme(array('forum__' . $tid, 'forum'), $forum)
 *     @endcode
 *   - preprocess functions: A list of functions used to preprocess this data.
 *     Ordinarily this won't be used; it's automatically filled in. By default,
 *     for a module this will be filled in as template_preprocess_HOOK. For
 *     a theme this will be filled in as phptemplate_preprocess and
 *     phptemplate_preprocess_HOOK as well as themename_preprocess and
 *     themename_preprocess_HOOK.
 *   - override preprocess functions: Set to TRUE when a theme does NOT want the
 *     standard preprocess functions to run. This can be used to give a theme
 *     FULL control over how variables are set. For example, if a theme wants
 *     total control over how certain variables in the page.tpl.php are set,
 *     this can be set to true. Please keep in mind that when this is used
 *     by a theme, that theme becomes responsible for making sure necessary
 *     variables are set.
 *   - type: (automatically derived) Where the theme hook is defined:
 *     'module', 'theme_engine', or 'theme'.
 *   - theme path: (automatically derived) The directory path of the theme or
 *     module, so that it doesn't need to be looked up.
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 */
function hook_theme($existing, $type, $theme, $path) {
  return array(
    'forum_display' => array(
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      'variables' => array('forums' => NULL, 'topics' => NULL, 'parents' => NULL, 'tid' => NULL, 'sortby' => NULL, 'forum_per_page' => NULL),
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    ),
    'forum_list' => array(
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      'variables' => array('forums' => NULL, 'parents' => NULL, 'tid' => NULL),
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    ),
    'forum_topic_list' => array(
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      'variables' => array('tid' => NULL, 'topics' => NULL, 'sortby' => NULL, 'forum_per_page' => NULL),
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    ),
    'forum_icon' => array(
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      'variables' => array('new_posts' => NULL, 'num_posts' => 0, 'comment_mode' => 0, 'sticky' => 0),
    ),
    'status_report' => array(
      'render element' => 'requirements',
      'file' => 'system.admin.inc',
    ),
    'system_date_time_settings' => array(
      'render element' => 'form',
      'file' => 'system.admin.inc',
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    ),
  );
}

/**
 * Alter the theme registry information returned from hook_theme().
 *
 * The theme registry stores information about all available theme hooks,
 * including which callback functions those hooks will call when triggered,
 * what template files are exposed by these hooks, and so on.
 *
 * Note that this hook is only executed as the theme cache is re-built.
 * Changes here will not be visible until the next cache clear.
 *
 * The $theme_registry array is keyed by theme hook name, and contains the
 * information returned from hook_theme(), as well as additional properties
 * added by _theme_process_registry().
 *
 * For example:
 * @code
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 * $theme_registry['user_profile'] = array(
 *   'variables' => array(
 *     'account' => NULL,
 *   ),
 *   'template' => 'modules/user/user-profile',
 *   'file' => 'modules/user/user.pages.inc',
 *   'type' => 'module',
 *   'theme path' => 'modules/user',
 *   'preprocess functions' => array(
 *     0 => 'template_preprocess',
 *     1 => 'template_preprocess_user_profile',
 *   ),
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 * );
 * @endcode
 *
 * @param $theme_registry
 *   The entire cache of theme registry information, post-processing.
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 *
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 * @see hook_theme()
 * @see _theme_process_registry()
 */
function hook_theme_registry_alter(&$theme_registry) {
  // Kill the next/previous forum topic navigation links.
  foreach ($theme_registry['forum_topic_navigation']['preprocess functions'] as $key => $value) {
    if ($value = 'template_preprocess_forum_topic_navigation') {
      unset($theme_registry['forum_topic_navigation']['preprocess functions'][$key]);
    }
  }
}

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/**
 * Return the machine-readable name of the theme to use for the current page.
 *
 * This hook can be used to dynamically set the theme for the current page
 * request. It overrides the default theme as well as any per-page or
 * per-section theme set by the theme callback function in hook_menu(). This
 * should be used by modules which need to override the theme based on dynamic
 * conditions.
 *
 * Since only one theme can be used at a time, the last (i.e., highest
 * weighted) module which returns a valid theme name from this hook will
 * prevail.
 *
 * @return
 *   The machine-readable name of the theme that should be used for the current
 *   page request. The value returned from this function will only have an
 *   effect if it corresponds to a currently-active theme on the site.
 */
function hook_custom_theme() {
  // Allow the user to request a particular theme via a query parameter.
  if (isset($_GET['theme'])) {
    return $_GET['theme'];
  }
}

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/**
 * Register XML-RPC callbacks.
 *
 * This hook lets a module register callback functions to be called when
 * particular XML-RPC methods are invoked by a client.
 *
 * @return
 *   An array which maps XML-RPC methods to Drupal functions. Each array
 *   element is either a pair of method => function or an array with four
 *   entries:
 *   - The XML-RPC method name (for example, module.function).
 *   - The Drupal callback function (for example, module_function).
 *   - The method signature is an array of XML-RPC types. The first element
 *     of this array is the type of return value and then you should write a
 *     list of the types of the parameters. XML-RPC types are the following
 *     (See the types at http://www.xmlrpc.com/spec):
 *       - "boolean": 0 (false) or 1 (true).
 *       - "double": a floating point number (for example, -12.214).
 *       - "int": a integer number (for example,  -12).
 *       - "array": an array without keys (for example, array(1, 2, 3)).
 *       - "struct": an associative array or an object (for example,
 *          array('one' => 1, 'two' => 2)).
 *       - "date": when you return a date, then you may either return a
 *          timestamp (time(), mktime() etc.) or an ISO8601 timestamp. When
 *          date is specified as an input parameter, then you get an object,
 *          which is described in the function xmlrpc_date
 *       - "base64": a string containing binary data, automatically
 *          encoded/decoded automatically.
 *       - "string": anything else, typically a string.
 *   - A descriptive help string, enclosed in a t() function for translation
 *     purposes.
 *   Both forms are shown in the example.
 */
function hook_xmlrpc() {
  return array(
    'drupal.login' => 'drupal_login',
    array(
      'drupal.site.ping',
      'drupal_directory_ping',
      array('boolean', 'string', 'string', 'string', 'string', 'string'),
      t('Handling ping request'))
  );
}

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/**
 * Alter the definition of XML-RPC methods before they are called.
 *
 * This hook lets at module modify the callback definition for already
 * declared XML-RPC methods, when they are being invoked by a client.
 *
 * This hook is invoked by xmlrpc.php. The method definitions are
 * passed in by reference. Each element of the $methods array is one
 * callback definition returned by a module from hook_xmlrpc. Additional
 * methods may be added, or existing items altered.
 *
 * Modules implementing this hook must take care of the fact that
 * hook_xmlrpc allows two distinct and incompatible formats for callback
 * definition, so module must be prepared to handle either format for
 * each callback being altered.
 *
 * @param $methods
 *   Associative array of method callback definitions returned from
 *   hook_xmlrpc.
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 *
 * @see hook_xmlrpc()
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 */
function hook_xmlrpc_alter(&$methods) {

  // Direct update for methods defined the simple way
  $methods['drupal.login'] = 'mymodule_login';

  // Lookup update for methods defined the complex way
  foreach ($methods as $key => &$method) {
    if (!is_int($key)) {
      continue;
    }
    if ($method[0] == 'drupal.site.ping') {
      $method[1] = 'mymodule_directory_ping';
    }
  }
}

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/**
 * Log an event message
 *
 * This hook allows modules to route log events to custom destinations, such as
 * SMS, Email, pager, syslog, ...etc.
 *
 * @param $log_entry
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 *   An associative array containing the following keys:
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 *   - type: The type of message for this entry. For contributed modules, this is
 *     normally the module name. Do not use 'debug', use severity WATCHDOG_DEBUG instead.
 *   - user: The user object for the user who was logged in when the event happened.
 *   - request_uri: The Request URI for the page the event happened in.
 *   - referer: The page that referred the use to the page where the event occurred.
 *   - ip: The IP address where the request for the page came from.
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 *   - timestamp: The UNIX timestamp of the date/time the event occurred
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 *   - severity: One of the following values as defined in RFC 3164 http://www.faqs.org/rfcs/rfc3164.html
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 *     WATCHDOG_EMERGENCY Emergency: system is unusable
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 *     WATCHDOG_ALERT     Alert: action must be taken immediately
 *     WATCHDOG_CRITICAL  Critical: critical conditions
 *     WATCHDOG_ERROR     Error: error conditions
 *     WATCHDOG_WARNING   Warning: warning conditions
 *     WATCHDOG_NOTICE    Notice: normal but significant condition
 *     WATCHDOG_INFO      Informational: informational messages
 *     WATCHDOG_DEBUG     Debug: debug-level messages
 *   - link: an optional link provided by the module that called the watchdog() function.
 *   - message: The text of the message to be logged.
 */
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function hook_watchdog(array $log_entry) {
  global $base_url, $language;
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  $severity_list = array(
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    WATCHDOG_EMERGENCY => t('Emergency'),
    WATCHDOG_ALERT     => t('Alert'),
    WATCHDOG_CRITICAL  => t('Critical'),
    WATCHDOG_ERROR     => t('Error'),
    WATCHDOG_WARNING   => t('Warning'),
    WATCHDOG_NOTICE    => t('Notice'),
    WATCHDOG_INFO      => t('Info'),
    WATCHDOG_DEBUG     => t('Debug'),
</