D Programming Language source (dmd, phobos, etc.) has moved to github

[Nick Sabalausky]

"Ulrik Mikaelsson" <ulrik.mikaelsson at gmail.com> wrote in message 
news:mailman.949.1295999711.4748.digitalmars-d-announce at puremagic.com...
> Again, version-number + repo is not 100% when history-rewrite is possible.

"History-rewrite" is new to me. Does that just mean branching off from a 
past revision? If not, do you have a link that explains it?