Please add <group> → <generic>

This is a part of: #200

Preamble

The ordering model defined in #194 requires clear identification of generic families. As far as I know (but I may be wrong), fontconfig does not know what its generics are today – they are just substitution patterns that happen to never match real font files.

Purpose

Using generic instead of target makes an group block a generic declaration.

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- SPDX-License-Identifier: MIT -->
<fontconfig>
  <group>
    <generic>@generic_family_name@</generic>
  </group>
</fontconfig>

Behaviour

generic is incompatible with target. The group blocks for a font family can either contain generic or target but not both (both is a syntax error).

generic is incompatible with family and match. A generic, is not supposed to match real font files.

fontconfig rejects any font file, that declares a generic name, as its family (unless remapped to something else in another group block).

A fontconfig command returns the list of generics known to a fontconfig installation, so users can query the classification model in use before writing new fontconfig rules (similar to the way iconv --list returns the encoding names it currently understands).

The top level group + like declaration for a given generic family, corresponds to the default system fonts.

Minimal example

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- SPDX-License-Identifier: MIT -->
<fontconfig>
  <group>
    <generic>serif</generic>
    <like>
      <family>DejaVu Serif</family>
      <family>Noto Serif</family>
    </like>
  </group>
</fontconfig>