Rev4 update

This is in sync with https://docs.google.com/document/d/1m7Cep2U5eCe5M62Y6a_4CNGF7QM4UgJtmMFq2FrRo3s/edit?usp=sharing

and implements the proposals there. Please carefully review (in particular removed messages). This will go soon in master after another community review round. Criticism now or never 8).