How to use /etc/yum/vars/* ?

In the man page for yum.conf there is a note that reads..

  "As of 3.2.28, any file in /etc/yum/vars is turned into a variable named
   after the filename (or overrides any of the above variables)."

How do I use this?  I'm guessing that maybe I make a file called
/etc/yum/vars/FOOBAR and have it output a string to stdout
 and then inside yum.conf  I can use a macro called $FOOBAR

Is this documented any place other then what I quoted above?
If I figure this out I'll be happy to submit a man page patch.
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Chris Albertson
Redondo Beach, California