  observer: '_invalidChanged',
        type: Boolean,
        value: false
      },

      /**
       * True if the input has focus.
       */
      focused: {
        readOnly: true,
        type: Boolean,
        value: false,
        notify: true
      },

      _addons: {
        type: Array
        // do not set a default value here intentionally - it will be initialized lazily when a
        // distributed child is attached, which may occur before configuration for this element
        // in polyfill.