Thank you for these explanations. I’ve looked up Winipedia on the keywords too, and that there is OpenType glyph substitution. Probably that means that the user has to produce the raw text file and formatting instructions, and the rest is done by the font and the rendering engine, like when we use fraction formatiing and typographic ligatures, that are generated within the word processing software and the font, and not input as characters, the ff, fi, fl, ffi, ffl in Unicode being for legacy support only (for Word).
Marcel