code: function (type, args, obj) {
  
              var val = args[0],
                  alreadySubscribed = Config.alreadySubscribed,
                  windowResizeEvent = Overlay.windowResizeEvent,
                  windowScrollEvent = Overlay.windowScrollEvent;
  
              if (val) {
                  this.center();
  
                  if (!alreadySubscribed(this.beforeShowEvent, this.center)) {
                      this.beforeShowEvent.subscribe(this.center);
                  }
  
                  if (!alreadySubscribed(windowResizeEvent, this.doCenterOnDOMEvent, this)) {
                      windowResizeEvent.subscribe(this.doCenterOnDOMEvent, this, true);
                  }
  
                  if (!alreadySubscribed(windowScrollEvent, this.doCenterOnDOMEvent, this)) {
                      windowScrollEvent.subscribe(this.doCenterOnDOMEvent, this, true);
                  }
  
              } else {
                  this.beforeShowEvent.unsubscribe(this.center);
  
                  windowResizeEvent.unsubscribe(this.doCenterOnDOMEvent, this);
                  windowScrollEvent.unsubscribe(this.doCenterOnDOMEvent, this);
              }
          }
docs: The default event handler fired when the "fixedcenter" property
  is changed.
  @method configFixedCenter
  @param {String} type The CustomEvent type (usually the property name)
  @param {Object[]} args The CustomEvent arguments. For configuration
  handlers, args[0] will equal the newly applied value for the property.
  @param {Object} obj The scope object. For configuration handlers,
  this will usually equal the owner.