I added an error message if "this" is not bound.

This function must be called directly (callStack.validateSize()), or with the callStack context bound!

I ran into this, but it being opaque, I wrote it off as probably having done something wrong myself ( I was doing wrong plenty ). In a later attempt it was not a problem - because I accidentally was in the correct scope.

Should be simple enough to fix by passing user a function bound to the correct context. ( Famous last words .. )