Returns whether or not an action hook is currently being processed.

The function current_action() only returns the most recent action being executed.
did_action() returns the number of times an action has been fired during
the current request.

This function allows detection for any action currently being executed
(regardless of whether it’s the most recent action to fire, in the case of
hooks called from hook callbacks) to be verified.

function doing_action( $hook_name = null ) {
	return doing_filter( $hook_name );
}