February 11, 2011 
Definition:
function add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {}
Hooks a function or method to a specific filter action.
Filters are the hooks that WordPress launches to modify text of various types before adding it to the database or sending it to the browser screen. Plugins 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.
Parameters
- string $tag: The name of the filter to hook the $function_to_add to.
- callback $function_to_add: The name of the function to be called when the filter is applied.
- 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.
- int $accepted_args: optional. The number of arguments the function accept (default 1).
Return values
returns:true
Source code
function add_filter($tag, $function_to_add, $priority = 10, $accepted_args = 1) {
global $wp_filter, $merged_filters;
$idx = _wp_filter_build_unique_id($tag, $function_to_add, $priority);
$wp_filter[$tag][$priority][$idx] = array('function' => $function_to_add, 'accepted_args' => $accepted_args);
unset( $merged_filters[ $tag ] );
return true;
}
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