The way they talk about it makes it sound like they invented the written word, but that notwithstanding the fonts actually look really nice in my opinion.
Contextual alternates are normally used for certain scripts, like Arabic, where the shape of each glyph depends on the surrounding glyphs. And they are also used for cursive handwriting fonts where the stroke of the “pen” might have different connection points across letters. Texture healing is a novel application of this technology to code.
basically fonts were already capable of using alternate versions of characters based on their nearby characters, so they used that for these fonts to allow for seemingly-dynamic sizing/spacing
This swapping is powered by an OpenType feature called “contextual alternates,” which is widely supported by both operating systems and browser engines.
Do modern IDEs allow for setting different fonts for comments, human written code, Copilot written code, etc? I don't do much actual coding these days, so it's been a while. I'm used to just seeing different colors but for things like comments and reserved words, but not fonts like they showed in the examples.