Documentation for syntax: mirrorlist=http://...?..& ?

Hello all:

I can't seem to find the documentation for the syntax for the following
line in a *.repo file:


mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os

Before I download the yum source and look at the code, I was hoping
someone could point me to a URL/man page/ that explains:
      * The '?'
      * The '&'
      * All the '='s

I know about the generic $xxx variables.

Thanks, I'm running yum 3.2.8 on Fedora 7 which appears to be the
current stable version.

thanks in advance
tc

-- 
tom campbell <[email protected]>
Dinkum Software