Too many Xorg modes

[Perry Hutchison]

In 6.1, how would I set up xorg.conf to restrict Xorg to a few
specific modes?  The Xorg.8.log created during xorgcfg shows 24
modelines, but when I cycle through the modes using CtrlAltPlus
there are two which don't work at all and the remaining 22 cover
only 8 resolutions (of which only about 3 seem likely to actually
be useful.)

A search for "modeline" in the docs and manpages turned up nothing
applicable beyond xorg.conf(5), which does not describe how to
prevent the implicit inclusion of built-in modes whose names do
not match any explicitly-specified modes.