rem: this.observers.push(observer); 
add: this.observers.push(observer); this._cacheObserverCallbacks(); 
context:   addObserver: function(observer) {    this.observers.push(observer);      },
meta: 3991	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/3991/d29159eae8749c508d01bb447868321a3ba6bbfa/dragdrop.js/buggy/manager/media/script/scriptaculous/dragdrop.js