man yum.conf ...

       installonly_limit
              Number of packages listed in installonlypkgs to  keep  installed
              at the same time. Setting to 0 disables this feature. Default is
              3.

Any chance you can add the word kernel there so that we can search for it?
e.g.

       installonly_limit
              Number of packages listed in installonlypkgs to  keep  installed
              at the same time. Setting to 0 disables this feature. Default is
              3. Often used to limit number of installed kernels.

 Just above that we have:

       installonlypkgs
              List  of  packages  that  should  only  ever be installed, never
              updated. Kernels in particular fall into this category. Defaults
              to kernel, kernel-smp, kernel-bigmem, kernel-enterprise, kernel-
              debug, kernel-unsupported.

I don't want to be rude here, but I think we're overthinking it.

If I want to find a config option that has disappeared, I will search for it in the man page and the config file. yum.conf makes no mention of it. I searched in the man page and found installonlypkgs, but I know this is not what I wanted. A helpful message on intstallonly_limit would make it findable.

Your man page, just my suggestion.