public static function add_hook( $when, $callback ) {
		if ( array_key_exists( $when, self::$hooks_passed ) ) {
			self::debug(
				sprintf(
					'Immediately invoking on passed hook "%s": %s',
					$when,
					Utils\describe_callable( $callback )
				),
				'hooks'
			);
			call_user_func_array( $callback, (array) self::$hooks_passed[ $when ] );
		}

		self::$hooks[ $when ][] = $callback;
	}