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Excerpts from internet.info-andrew: 24-Jun-91 Re: my menubar preferences
Michael McInerny@andrew. (514+0)

> Actually, what one really needs is a way to ask about the display (the
> one pointed to by $DISPLAY): 

> ?DisplayClass=Color:...

> or

> ?DisplaySize=1280x1024:...

> or

> ?DisplayResolution=75:...

> Does this seem like a reasonable proposal?

\begin{slipperyslope}

This reminds me a lot of the discussions that led to the "?M=", etc.
syntax in the first place.  Eventually, I added in a "?E=" (for things
dependent on environment variables) because the predefined things like
machine type & name were just not enough.  I'm not sure you want to
enumerate all the desired possibilities, either.  Instead, one
possibility is a more general mechanism in which a command is executed
and its exit status determines whether or not the preference should be
read.  For example:

?X=/u/nsb/bin/iscolor: some-preference

would execute the /u/nsb/bin/iscolor program and have some-preference
take effect only if it returns a non-zero value.  You might also want to
hardwire some of the more common ones, like the ones Mike mentions, but
there will be a never-ending stream of them.

However, this is (obviously) not very efficient.  But why do we need any
changes at all?  You can do the "right thing" today, with no code
changes, if you really want.  Add the code to .xinitrc that checks
whatever you want and sets an environment variable, e.g.

if (big-hairy-test) then
    setenv ISCOLOR 1
else
    setenv ISCOLOR 0
endif

and then have preferences of the form

?E=ISCOLOR=1: whatever

I believe that this approach will work for you today, without going any
further down the slippery slope of hard-wired preference options.... --
Nathaniel