[Fedora-packaging] forbid fedora or redhat in spec files?

Hello, I have seen people saying that we should avoid using 'fedora' and 'redhat' in spec files, to help reusing in other contexts (be it, selfishly, EPEL/RHEL/OLPC, or other distros or upstreams). I think it is a good idea, especially since there is a trademark on fedora and redhat (unless I am wrong). Should we have a guideline about that? Or on a 'trick' page? -- Pat