the $observe function

http://docs.angularjs.org/guide/directive#attributes

angularjs/angular.d.ts

@@ -119,6 +119,7 @@ declare module ng {
     ///////////////////////////////////////////////////////////////////////////
     interface IAttributes {
         $set(name: string, value: any): void;
+        $observe(name: string, fn:(value?:any)=>any):void;
         $attr: any;
     }