atio: {
        type: Number,
        value: 0,
        readOnly: true
      },

      /**
       * Use an indeterminate progress indicator.
       */
      indeterminate: {
        type: Boolean,
        value: false,
        observer: '_toggleIndeterminate'
      },

      /**
       * True if the progress is disabled.
       */
      disabled: {
        type: Boolean,
        value: false,
        reflectToAttribute: true,
        observer: '_disabledChanged'
      }
    },

    observers: [
      '_prog