http-protocol question

In Documentation/technical/http-protocol.txt, there is the following statement:

"S: Parse the git-upload-pack request:

Verify all objects in `want` are directly reachable from refs.

The server MAY walk backwards through history or through the reflog to permit slightly stale requests."

Is there actually logic somewhere in Git that does that "MAY walk backwards" step? Or is that something another implementation of Git may do but the standard Git does not?

Thanks, Bryan Turner