vojtajina/angular.js — comment on commit 97d68900b73641c9629a6989edfdc82a87c4c49a
File: src/service/scope.js line 593
By vojtajina:

That's the purpose of this CL - expose this property, so that the guy who fired the event knows, whether it was cancelled or not.
(YouTube requirement - they are currently monkey patching scope.__proto__ to get this information...)