under X: instead of having two separate fixed-width fonts one of
which is twice the width of the other, you can instead have a single
font in which some characters are twice as wide as others.
This is implemented very simply: if you specify a wide font, it will
be used for wide characters, and if you don't then the normal font
will be used for wide characters (so they'd better _be_ wide in that
font, or there'll be trouble).
I got this idea from Jed, whose latest version supports UTF-8 and
requires a font of this type. If there are going to be X fonts like
that kicking around, there will doubtless be people who want to use
them.
[originally from svn r6844]