Wanted: hg branch -r REV

I want the following in Mercurial: -r REV argumn for hg branch.

Default "hg branch" is equivalnt to "hg branch -r ."

Branch of some other REV is "hg branch -r REV"

Actually, what I really want is this in revsets: "hg log -r "branch_of(.)"

Then I could do: hg log -r "max(ancestors(.) and not branch(branch_of(.)))"

- the most recent ancestor on a different branch

Ah: matching (just not in the version a work).  But it is not quite on...  it returns revs, not branch