[Zope] question about copyng btree elements

[Yuri]

Hi!

I've a Zope BTree called answers. It contains PersistentMapping objects:

self.answers[userid] = PersistentMapping(value=value,
                                                 comments=comments)

value can be a string, a list or a dictionary

what happen exactly if I do: question.answers[a_userdid] = 
question.answers[another_user_id] ?

 From my (poor) tests they seems not to share anything, I mean I can 
modify question.answers[a_userdid] and question.answers[another_user_id] 
is untouched.

Is this true? Should I beware of something?