Clean up the documentation for add_filter and apply_filters.

Fixes #19203 props DrewAPicture, ericlewis


git-svn-id: https://develop.svn.wordpress.org/trunk@25476 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/plugin.php

@@ -22,44 +22,46 @@
 /**
  * Hooks a function or method to a specific filter action.
  *
- * Filters are the hooks that WordPress launches to modify text of various types
+ * WordPress offers filter hooks to allow plugins to modify
- * before adding it to the database or sending it to the browser screen. Plugins
+ * various types of internal data at runtime.
- * can specify that one or more of its PHP functions is executed to
- * modify specific types of text at these times, using the Filter API.
  *
- * To use the API, the following code should be used to bind a callback to the
+ * A plugin can modify data by binding a callback to a filter hook. When the filter
- * filter.
+ * is later applied, each bound callback is run in order of priority, and given
+ * the opportunity to modify a value by returning a new value.
+ *
+ * The following example shows how a callback function is bound to a filter hook.
+ * Note that $example is passed to the callback, (maybe) modified, then returned:
  *
  * <code>
- * function example_hook($example) { echo $example; }
+ * function example_callback( $example ) {
- * add_filter('example_filter', 'example_hook');
+ * 	// Maybe modify $example in some way
+ * 	return $example;
+ * }
+ * add_filter( 'example_filter', 'example_callback' );
  * </code>
  *
- * In WordPress 1.5.1+, hooked functions can take extra arguments that are set
+ * Since WordPress 1.5.1, bound callbacks can take as many arguments as are
- * when the matching do_action() or apply_filters() call is run. The
+ * passed as parameters in the corresponding apply_filters() call. The $accepted_args
- * $accepted_args allow for calling functions only when the number of args
+ * parameter allows for calling functions only when the number of args match.
- * match. Hooked functions can take extra arguments that are set when the
- * matching do_action() or apply_filters() call is run. For example, the action
- * comment_id_not_found will pass any functions that hook onto it the ID of the
- * requested comment.
  *
- * <strong>Note:</strong> the function will return true no matter if the
+ * <strong>Note:</strong> the function will return true whether or not the callback
- * function was hooked fails or not. There are no checks for whether the
+ * is valid. It is up to you to take care. This is done for optimization purposes,
- * function exists beforehand and no checks to whether the <tt>$function_to_add</tt>
+ * so everything is as quick as possible.
- * is even a string. It is up to you to take care and this is done for
- * optimization purposes, so everything is as quick as possible.
  *
  * @package WordPress
  * @subpackage Plugin
- * @since 0.71
+ *
- * @global array $wp_filter Stores all of the filters added in the form of
+ * @global array $wp_filter      A multidimensional array of all hooks and the callbacks hooked to them.
- *	wp_filter['tag']['array of priorities']['array of functions serialized']['array of ['array (functions, accepted_args)']']
  * @global array $merged_filters Tracks the tags that need to be merged for later. If the hook is added, it doesn't need to run through that process.
  *
- * @param string $tag The name of the filter to hook the $function_to_add to.
+ * @since 0.71
- * @param callback $function_to_add The name of the function to be called when the filter is applied.
+ *
- * @param int $priority optional. Used to specify the order in which the functions associated with a particular action are executed (default: 10). Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.
+ * @param string   $tag             The name of the filter to hook the $function_to_add callback to.
- * @param int $accepted_args optional. The number of arguments the function accept (default 1).
+ * @param callback $function_to_add The callback to be run when the filter is applied.
+ * @param int      $priority        (optional) The order in which the functions associated with a particular action are executed. Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.
+ *                                  Default 10.
+ * @param int      $accepted_args   (optional) The number of arguments the function accepts.
+ *                                  Default 1.
  * @return boolean true
  */
 function add_filter( $tag, $function_to_add, $priority = 10, $accepted_args = 1 ) {
@@ -114,24 +116,33 @@ function has_filter($tag, $function_to_check = false) {
  *
  * The function allows for additional arguments to be added and passed to hooks.
  * <code>
- * function example_hook($string, $arg1, $arg2)
+ * // Our filter callback function
- * {
+ * function example_callback( $string, $arg1, $arg2 ) {
- *		//Do stuff
+ *	// (maybe) modify $string
  *	return $string;
  * }
- * $value = apply_filters('example_filter', 'filter me', 'arg1', 'arg2');
+ * add_filter( 'example_filter', 'example_callback', 10, 3 );
+ *
+ * // Apply the filters by calling the 'example_callback' function we
+ * // "hooked" to 'example_filter' using the add_filter() function above.
+ * // - 'example_filter' is the filter hook $tag
+ * // - 'filter me' is the value being filtered
+ * // - $arg1 and $arg2 are the additional arguments passed to the callback.
+ * $value = apply_filters( 'example_filter', 'filter me', $arg1, $arg2 );
  * </code>
  *
  * @package WordPress
  * @subpackage Plugin
- * @since 0.71
+ *
  * @global array $wp_filter         Stores all of the filters
  * @global array $merged_filters    Merges the filter hooks using this function.
  * @global array $wp_current_filter stores the list of current filters with the current one last
  *
+ * @since 0.71
+ *
  * @param string $tag  The name of the filter hook.
  * @param mixed $value The value on which the filters hooked to <tt>$tag</tt> are applied on.
- * @param mixed $var,... Additional variables passed to the functions hooked to <tt>$tag</tt>.
+ * @param mixed $var   Additional variables passed to the functions hooked to <tt>$tag</tt>.
  * @return mixed The filtered value after all hooked functions are applied to it.
  */
 function apply_filters( $tag, $value ) {
@@ -708,7 +719,6 @@ function register_uninstall_hook( $file, $callback ) {
  * @uses $wp_filter Used to process all of the functions in the 'all' hook
  *
  * @param array $args The collected parameters from the hook that was called.
- * @param string $hook Optional. The hook name that was used to call the 'all' hook.
  */
 function _wp_call_all_hook($args) {
 	global $wp_filter;