What is 6.0-BETA4?

[Gary W. Swearingen]

That is, what event created it and, if it is a changing thing,
what event will cause it to stop changing?

I'm guessing from the announcement which says that one can get it from
from the RELENG_6 CVS branch, that it is a generic name for any OS
made from RELENG_6 between its announcement and the later announcement
of a so-called 6.0 release candidate.  Correct?  Or are there some
kind of markers in the CVS?  Or...?

And do release candidates have their own actual CVS branches and tags?