Following up on a note form @HansMuller :)

I'm working on a SliverAppBar feature and was just looking at https://api.flutter.dev/flutter/material/SliverAppBar/onStretchTrigger.html. I wasn't sure what it was for. You wrote a beautiful example in #42250. Someday it might be nice to include it in the API docs.