From Fedora Project Wiki
On "Note for RHN Users"
I'm wondering if the advice to add 'optional' should be a bit more explicit. AFAIK, it's telling me 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".