public function register_parent_results($function_name, $bucket = self::DEFAULT_BUCKET)
	{
		// call parent function
		if ( is_callable($function_name) || ( is_array($function_name) && method_exists($function_name[0], $function_name[1]) ) || method_exists($this, $function_name) || function_exists($function_name) )
		{
			$this->parent_function_results[$bucket] = $function_name;
			return true;
		}

		return false;
	}