[[!comment format=mdwn
 username="joey"
 subject="""comment 1"""
 date="2015-09-09T18:34:29Z"
 content="""
It's hard to add this kind of thing to the preferred content expressions.

First, it would be quite slow to check if a given key
was present in some file in a given branch. There's no index for that
information.

Second, even if that were implemented, there's no guarantee at all that
different repositories have the same git branches. If repo Foo wants files in
branch B, and repo Bar sees that, and has no branch B, or a different
version of branch B, how is it supposed to know which files to send to
repo Foo?

So, I can see the use case, but I don't see how preferred content can
support it.
"""]]