andrewplummer/Sugar — comment on commit 849edd92844efdd821da27b6a3063ec4ece941dc
File: lib/core.js line 343
By andrewplummer:

Now that I'm mapping methods directly onto the object there has to be some flag that can tell if the object has been extended or not.... (I don't want to depend on any one method), so I can't see a way around mapping this flag onto the object...

Note that this property will be non-enumerable in most browsers but not all so it very well may be "visible", even if collisions are unlikely...