[Fontconfig] Request for implementing font substitution for CJK fonts

[Nicolas Mailhot]

Hi,

What we do in Fedora is shipping fallback rules with the font themselves in
the same package so if font foo is installed the package also declares to
fontconfig it's an acceptable substitute for bar, but if the user didn't
install foo the system does not waste time processing rules for fonts which
are not available.

And BTW it's very dangerous to declare a substitution rule for a popular font,
because your substitution font will then be used in lots of contexts and if
it's not as good (design or coverage-wise) as the original font users won't be
happy at all.

-- 
Nicolas Mailhot