Multiple Substitution With Classes

Glyphs allows multiple substitution (one-to-many) to use classes instead of just single glyphs. This works for both simple and contextual rules:

sub @Symbol by @SymbolLeft @SymbolRight;
sub @Left @Symbol' @Right by @SymbolLeft @SymbolRight;

The class that gets substituted (@Symbol in the example above) needs to have the same number of glyphs as the classes that it gets substituted by (@SymbolLeft, @SymbolRight).

If there is a single glyph or a class containing a single glyph on either side of the substitution rule, that glyph is repeated to match the count of the other classes in the substitution.