[Zope] Developing 'products' for zope 4 and 5

Hi, I am trying to catch up with the innovation that zope has undergone (I still have an instance running under zope 2.10.9). Is there any more extensive documentation on how to develop ‘products’ for zope 4 and 5. In the Zope Developer’s Guide the chapter on Zope products simply starts with the remark that the document is currently being reviewed. best, cb