- <<def_ref,ref>> and local ref. They are combined with a colon in
- the format <src>:<dst>, preceded by an optional plus sign, +.
- For example: `git fetch $URL
- refs/heads/master:refs/heads/origin` means "grab the master
- <<def_branch,branch>> <<def_head,head>> from the $URL and store
- it as my origin branch head". And `git push
- $URL refs/heads/master:refs/heads/to-upstream` means "publish my
- master branch head as to-upstream branch at $URL". See also
- linkgit:git-push[1].