code: function( event ) {
  		// left mouse button or tap
  		if( event.button === 0 || event.type === 'touchstart' ) {
  			this.header.parent.setActiveContentItem( this.contentItem );
  			
  		// middle mouse button
  		} else if( event.button === 1 && this.contentItem.config.isClosable ) {
  			this._onCloseClick( event );
  		}
  	}
docs: Callback when the tab is clicked
  
  @param {jQuery DOM event} event
  
  @private
  @returns {void}