his is set, the label will always float.
       */
      placeholder: {
        type: String,
        // need to set a default so _computeAlwaysFloatLabel is run
        value: ''
      },

      /**
       * Bind this to the `<input is="iron-input">`'s `readonly` property.
       */
      readonly: {
        type: Boolean,
        value: false
      },

      /**
       * Bind this to the `<input is="iron-input">`'s `size` property.
       */
      size: {
        type: Number
      },

      // Nonstandar