src/Shared/Message/Loader/LoaderAwareTrait.php
protected static function hasLoader(
        /*# bool */ $search = false
    ) {
        $class = get_called_class();

        if (isset(self::$loaders[$class])) {
            return $class;
        } elseif (__CLASS__ === $class) {
            return false;
        } elseif ($search) {
            $parent = get_parent_class($class);
            return $parent::hasLoader(true);
        }

        return false;
    }
protected static function hasLoader(
        /*# bool */ $search = false
    ) {
        $class = get_called_class();

        if (isset(self::$loaders[$class])) {
            return $class;
        } elseif (__CLASS__ === $class) {
            return false;
        } elseif ($search) {
            $parent = get_parent_class($class);
            return $parent::hasLoader(true);
        }

        return false;
    }
Check loader for calling message class (static bind)

if $search is true, search upwards in inhertiant tree for loader
if current class has no loader set

@param  bool $search search upwards
@return false|string false or classname for which has loader
@access protected