Except with explicit permission by a release manager.
Do whatever you want on develop, just don't change master.
We'll re-open master after the beta.
6-Mar: Boost 1.70.0 closed for all changes
13-Mar: Boost 1.70.0 beta; master branch re-opened
2-Aug: Release closed for all changes, except by permission of a release manager.
3-Apr: Boost 1.70.0 closed for all changes
10-Apr: Boost 1.70.0 release
-- The release managers