the first ancestor of the current commit, and the branch will start
out with no files. An unlimited number of `merge` commands per
commit are permitted by fast-import, thereby establishing an n-way merge.
-However Git's other tools never create commits with more than 15
-additional ancestors (forming a 16-way merge). For this reason
-it is suggested that frontends do not use more than 15 `merge`
-commands per commit; 16, if starting a new, empty branch.
Here `<commit-ish>` is any of the commit specification expressions
also accepted by `from` (see above).