[Zope] Product availability

[John Morton]

I'm having some trouble figuring out how to control where various products
are added in Zope.

I've added a Zclass inside a Zclass directory like product with the intent
that this class is only ever added inside instances of the first class.
Except that, ATM, I can't add instances of it anywhere.

I'd like to be able to use the same trick on a python product - it has
LinkFolderRoot, LinkFolder and Link classes, and ATM, you can add any of
them anywhere. I'd like to only be able to add LinkFolders and Link to
other LinkFolders and the LinkFolderRoot, be able to add a LinkFolderRoot
anywhere (but see below), and _not_ be able to add a LinkFolderRoot to
another LinkFolderRoot or LinkFolder (it all makes sense, trust me :-).

Finally, in the best of all possible worlds, I'd like to only be able to
add the LinkFolderRoot to a particular ZClass (the first one discussed, as
it happens). I suspect this isn't possible, though.

So, what are the necessary invokations, o Zope Masters?

John