As a special case, the `"@\{-N\}"` syntax for the N-th last branch
checks out the branch (instead of detaching). You may also specify
`-` which is synonymous with `"@\{-1\}"`.
++
+As a further special case, you may use `"A...B"` as a shortcut for the
+merge base of `A` and `B` if there is exactly one merge base. You can
+leave out at most one of `A` and `B`, in which case it defaults to `HEAD`.
<new_branch>::
Name for the new branch.
--onto option is not specified, the starting point is
<upstream>. May be any valid commit, and not just an
existing branch name.
++
+As a special case, you may use "A...B" as a shortcut for the
+merge base of A and B if there is exactly one merge base. You can
+leave out at most one of A and B, in which case it defaults to HEAD.
<upstream>::
Upstream branch to compare against. May be any valid commit,