  */
      selectedClass: {
        type: String,
        value: 'iron-selected'
      },

      /**
       * The attribute to set on elements when selected.
       */
      selectedAttribute: {
        type: String,
        value: null
      },

      /**
       * Default fallback if the selection based on selected with `attrForSelected`
       * is not found.
       */
      fallbackSelection: {
        type: String,
        value: null
      },

      /**
       * The list of items from which a selection