public function registerPseudoFilter($name, $object, $entity = "value")
    {
        if (is_callable($object)) {
            // user defined pseudo-filter
            $this->_pseudoFilters[$name] = array(
                "classname" => "CssParserFilterPseudoUserDefined",
                "user_def_function" => $object,
                "entity" => $entity
            );
        } else {
            $this->_pseudoFilters[$name] = array(
                "classname" => $object,
                "user_def_function" => null,
                "entity" => $entity
            );
        }
    }