[Fontconfig] Revisiting FcFontMatch and FcFontSort

[Lawrence D'Oliveiro]

On Tue, 23 Feb 2021 00:21:48 -0500, Matthias Clasen wrote:

> But what characters are reasonably 'covered' by font very much
> depends on what use the second step makes of the font. The harfbuzz
> shaper can decompose and compose glyphs and thereby extend coverage
> in ways that freetype has no idea about.

But shaping involves glyph substitution, not character substitution.
Those rules are supposed to only change the appearance of the text, not
its meaning (the actual characters of the text). For example, it would
not make sense for substitution rules to change “get” into “got”.

Though one exception I can think of is the rendering of flags for
ISO-3166 region codes in the special Unicode region-code range. Here
the coverage involves character pairs, not characters. Can this happen
with regular text?