code: function( a, b ) {
              this.id = b.attr('id');
              this.instances = [];
              this.element = b;
              this.options = jQuery.extend(this.options, a);
              this._create();
              if ( this._init ) {
                  this._init();
              }
          }
docs: Setup plugin basics,
  Set the jQuery UI Widget this.element, so extensions will work on both plugins