public function getModuleHandler()
    {
        if (is_null($this->_moduleHandler)) {
            $stem = $this->field;
            if (!isset(self::$_moduleHandlers[$stem])) {
                self::$_moduleHandlers[$stem] = [];
            }
            $n = count(self::$_moduleHandlers[$stem]);
            $this->_moduleHandler = $this->field . ':_' . $n;
            self::$_moduleHandlers[$stem][] = $this->_moduleHandler;
        }

        return $this->_moduleHandler;
    }