docs: function (cfg, ctxt, lineNumber) {
          this.$Button.constructor.apply(this, arguments);
  
          /**
           * Instance of the Icon widget used by this widget.
           * @type aria.widgets.Icon
           * @protected
           */
          this._icon = new ariaWidgetsIcon({
              icon : cfg.icon,
              sourceImage : cfg.sourceImage
          }, ctxt, lineNumber);
      }