OR not return the attribute.
Absolutely not. The user has asked for ALL attributes. Unless access controls prevent it, all should be returned, even if the user cant handle them. For example, pictures should be returned, even though today some well known windows clients cant display them (whilst others can).
I concur.
This is no different to sending others back using ;binary encoding. The server does not know what the client supports, so should assume it can support everything since it has not limited what it wants.
Yes.
Ciao, Michael.