[pikelet]

These are important typographical features and I'm fairly sure this is handled by font rendering libraries, not the browser (other than handling the CSS rules), so I can't imagine it's that difficult to implement? Correct me if I'm wrong!

[johncolanduoni]

It’s handled by text shaping libraries (e.g. Harfbuzz in Chrome and Firefox), not font rendering APIs (usually provided by the OS), but you have the right idea.