var $photo = $("#photo");var $trash = $("#trash");$("li").draggable({? revert: "invalid",? helper: "clone",? cursor: "move"});$trash.droppable({? accept: "#photo li",? activeClass: "highlight",? drop: function(event, ui){? ? abc(ui.draggable); ? ? ?//ui是什么東西，ui.draggable又是什么意思? }});