defined`,
       * the attribute will be removed (this is the default for boolean
       * type `false`).
       *
       * @param {Element} node Element to set attribute to.
       * @param {*} value Value to serialize.
       * @param {string} attribute Attribute name to serialize to.
       */
      _valueToNodeAttribute(node, value, attribute) {
        let str = this._serializeValue(value);
        if (str === undefined) {
          node.removeAttribute(attribute);
        } else {
          node.setAt