to auto-validate the input value when it changes.
       */
      autoValidate: {
        type: Boolean,
        value: false
      },

      /**
       * True if the input is invalid. This property is set automatically when the input value
       * changes if auto-validating, or when the `iron-input-validate` event is heard from a child.
       */
      invalid: {
        observer: '_invalidChanged',
        type: Boolean,
        value: false
      },

      /**
       * True if the input has focus.
     