code: function() {
          while ( this.currentOverlays.length > 0 ) {
              this.currentOverlays.pop().destroy();
          }
          THIS[ this.hash ].forceRedraw = true;
          /**
           * Raised when all overlays are removed from the viewer (see {@link OpenSeadragon.Drawer#clearOverlays}).
           *
           * @event clear-overlay
           * @memberof OpenSeadragon.Viewer
           * @type {object}
           * @property {OpenSeadragon.Viewer} eventSource - A reference to the Viewer which raised the event.
           * @property {?Object} userData - Arbitrary subscriber-defined object.
           */
          this.raiseEvent( 'clear-overlay', {} );
          return this;
      }
docs: Removes all currently configured Overlays from this Viewer and schedules
  an update.
  @method
  @return {OpenSeadragon.Viewer} Chainable.
  @fires OpenSeadragon.Viewer.event:clear-overlay