title: Mercurial: what are the consequences of changing a phase?
body: <p>In Mercurial, the phase of a revision can be changed arbitrarily. What are the consequences of a phase change for all possible transitions <em>(public, draft, secret) x (public, draft, secret)</em>? Which phase changes are safe? Which may cause troubles and which kind of troubles? Which are more or less no-ops?</p>