[RFC] Support for arbitrary tags in commits

Hello everybody,

I'd like to attach some additional data to commits.

The best way I've found (so far) is to put an additional header line in the commit header that references an additional blob.

Currently I've found "tree", "parent", "author", "committer", and so on; git accepts additional lines before the "\n\n" separator (and the commit message), so that's where I'd like to put the line.

"git fsck" allows that, too; only "rebase -i" and similar don't know about them (yet), and discard them.

Now I want to ask:
 * Is this acceptable?
 * If yes, I'd try to provide a patch to make "amend" and similar keep the
   header-lines (by collecting them in order - obviously with editing commits
   a header could exist multiple times).
 * Perhaps there should be an option for "git-commit" that inserts arbitrary
   header lines?
 * Is there some documentation for the commit-file format so that this can be
   written down?
 * How should namespace-issues be handled?
   I can imagine that multiple people want to put data there, how should the
   tag be allocated?
   This could be solved by the previous point, ie. there's some page that
   header tags should be registered at to avoid collisions.

Thank you for all feedback.

Regards,

Phil