老师，这一段代码不是很懂，可否详细讲解一下

$.fn.extend({

    search: function(option) {

        return this.each(function() {

            var $this=$(this),

            search=$this.data('search'),

            options = $.extend({}, Search.DEFAULTS, $(this).data(), typeof option==='object'&&option);

            // dropdown(this, options);  

            if(!search){//解决多次调用search问题

                $this.data('search',search=new Search($this,options));

            }  

            if(typeof search[option]==='function'){

                search[option]();

            }

        });

    }

});