From Fedora Project Wiki
On "Note for RHN Users"
I'm wondering if the advice to add 'optional' should be a bit more explicit about exact channel names. RHEL 6 channels have child channels with "optional" in the name, but RHEL5 ones don't.
AFAIK, I can only interpret it as an instruction to add something like "rhel-x86_64-server-productivity-5", which doesn't actually have the word "optional" appear in the channel name (at least in RHEL 5.version I'm using). The user must look at the descriptive name to know there's a reference to something "optional", and that word "optional" does not appear in the displayed child channel names for All Release Channels Page.