font substitution feature?

[Andrew Cassin]

Dear louters,

sorry if this can already be done (I just dont know it :-) but I would like
to see one additional feature - font & glyph substitution. I havent quite
worked out the right semantics for it, but you should be able to say "use
font xxx if font yyy is not available". I dont know whether
this would be done via the command line, a style file or whatever but
I think you should be able to do it.

This would make trying different document styles much easier.
Perhaps a warning that font substitution is taking place should be issues.

Secondly, if a glyph in a requested font is not available (at least according
to the available metrics file) you should be able to substitute a different
glyph from a different font. This is useful when working with partial fonts
in lout documents (such as a keycaps font or font specifically designed
for headings) so that special characters like punctuation still get rendered
and dont "magically disappear".

Is this easy/useful?

ACAS