       *
       * @param {Object} currentProps Bag of all current accessor values
       * @param {Object} changedProps Bag of properties changed since the last
       *   call to `_propertiesChanged`
       * @param {Object} oldProps Bag of previous values for each property
       *   in `changedProps`
       * @protected
       */
      _propertiesChanged(currentProps, changedProps, oldProps) { // eslint-disable-line no-unused-vars
      }

      /**
       * Method called to determine whether a property 