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The %{?repo} Tag
Most (but not all) RPM spec files will have a Release tag that contains
the following:
Release: %{?repo}N%{?dist}
where N is usually either a positive integer or is of the form
0.rcM or 0.devM where M is a positive integer.
The idea behind this added complexity to the Release tag is so that
different repositories can exist that have duplicate packages sometimes
even built from the same RPM spec file but with different capabilities.
These repositories can then have a hierarchal repo macro so that as
long as the Version is the same, the repository with the greater
repo tag will always resolve as the newer package to RPM.
This can help avoid things like GNU Emacs linked against X11 from being
replaced by a GNU Emacs package that is not linked against X11 just
because a “lower-level” package repository rebuilt GNU Emacs with a
larger N than the “higher-level” package repository uses.