So now we finally have some guidelines on how users should name their identifiers to be fairly future proof. This should hopefully help reduce the amount of pain people suffer when PHP adds new features like a class for Date or File handling. Although the two mentioned examples have settled on using DateTime and FileObject to get around the issue at least partially.
The guide itself is unfortunately spread over 3 pages, which does not seem to make sense since there is really not that much content there yet. Then again the guide may get expanded in the future. Anyways I recommend that every serious PHP programmer have a look at the guide. If there are any issues please let me (or the PHPDoc team) know. Otherwise make sure you adapt your internal CS to match this guide.
The guide talks about the naming of items in the global namespace (functions, classes, interfaces, etC), some rules to follow for internal identifiers, and some quick tips on naming to create pseudo-namespaces.