Except when they don't, or don't give enough context. A top-level comment here[0...

Except when they don't, or don't give enough context. A top-level comment here[0] gives an example where text was internally rendered to a bitmap prior to display, so a MS library was needed to hook the relevant API calls to get at the source text. Unfortunately (in this exceptional case), native UI toolkits aren't always as nice as webpage DOM. We'll probably start experiencing the same issue on the Web as soon as WebAssembly gets popular enough for people to develop UI toolkits on top of it.

[0] - https://news.ycombinator.com/item?id=23251509