bug#18077: 24.4.50; Info-quoted face should inherit default

[Stefan Monnier]

>> The expectations of someone reading online documentation.  Most online
>> documentation I can find don't use bold, italics, or colors to
>> distinguish "technical elements" like those that usually appear in
>> Info-quoted face.
> Such documentation also uses proportional fonts for standard body text.

Indeed.  But currently, we can't do that very well because refilling
Info text is between hard and impossible (there would be other hurdles,
but that's the most immediate one).

> How am I supposed to know what fonts are available on arbitrary systems?

You don't need to know that.  You just need to know what alternative
fonts are available on the system where you bumped into the problem.

> I can only say that on my Linux system there are various other fonts
> available.  Liberation Mono would probably be the one that is closest
> to Courier.

Great, thanks.  I see my (xft, scalable) "courier" here on my Debian
machines is coming from the "foundry" "ibm", but I don't really know how
to further track its origin (e.g. which package it comes from).

> But whether that font is widely installed, I do not know.

Doesn't matter: face-font-family-alternatives is designed specifically
to overcome those problems.

E.g. we should probably change Info-quoted to use family
"monospace-serif" and then add an entry to face-font-family-alternatives
like ("monospace-serif" "Liberation Mono" "courier" "CMU Typewriter
Text" "fixed").


        Stefan