rem: this.observers.push(observer); 
add: this.observers.push(observer); this._cacheObserverCallbacks(); 
context:   addObserver: function(observer) {    this.observers.push(observer);      },
meta: 3974	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/3974/af9adbf17404d887f31369756326b0109da7ae2b/dragdrop.js/buggy/root/static/js/dragdrop.js