The sexiest example I've seen is in the XState docs.. not sure what they're using to get the types into the tooltips.. https://stately.ai/docs/xstate/running-machines/react#usemac...
If you "inspect" the elements with the mouseovers, you can see they statically compiled the TS definition into the HTML.
I guess it probably uses the same APIs to read the types VSCode does, given what they state the purpose of Shiki is.