Matrix/Element support client-side widgets, like [Polls][polls].
polls are done 100% client-side, using ordinary events with the "m.poll" type.
unfortunately, that means the rendering is hard-coded into the client;
there's no generalizability.

widgets might be the generalization for polls.
documentation is scattered:
- `#matrix-widgets:matrix.org` to ask for help
- [aggregated links](https://github.com/vector-im/element-web/issues/20669#issuecomment-1367623830)
- ["widgets, the book"](https://github.com/matrix-org/matrix.org/pull/825/files)
- ["widgets, the spec"](https://github.com/matrix-org/matrix-spec-proposals/pull/2764)
- [widgets google doc](https://docs.google.com/document/d/1uPF7XWY_dXTKVKV7jZQ2KmsI19wn9-kFRgQ1tFQP7wQ/edit#heading=h.9rn9lt6ctkgi)
        - this is what the above links were based on
- [semi-official "sticker picker" example widget](https://github.com/matrix-org/simple-stickerpicker-widget)
- [Widget JS API/library](https://github.com/matrix-org/matrix-widget-api)
        - though, this might work *only* in the web version of Element?

[polls]: https://github.com/matrix-org/matrix-spec-proposals/blob/travis/msc/polls/proposals/3381-polls.md