As someone completely ignorant of the inner working of fonts, how is this different from ligatures? Those also produce special glyphs based on combinations.
>>vultou+(OP)
Yes this is exactly ligature, I just became aware that it was possible to use wasm for them in HarfBuzz, if you want to see some wasm examples that is not possible with ligatures have a look at https://github.com/harfbuzz/harfbuzz-wasm-examples