Subtree support?

[jdm]

Servo (the Rust-first embeddable web rendering engine) is very interested in exposing accessible web content to embedders using accesskit. Embedders can create any number of webviews, which could be rendered inside of a UI shell that already integrated accesskit. I'm interested in learning:

• is there already some discussion of how to support libraries like Servo that want to provide a subtree to library users to integrate into an existing accessibility tree?
• are there some next steps that I could assist with in supporting this use case?

The only reference I've seen to subtrees so far is in #504 (comment).

[mwcampbell]

Subtrees are complicated, and I haven't thought much about them yet. For Servo specifically, is the web content area always in its own platform-specific view (e.g. HWND on Windows, NSView on macOS, or android.view.View on Android)? Or is the web content sometimes rendered in the same platform view as the UI shell? I suppose this is more complicated on Linux, where the closest toolkit-independent thing to a platform view would be an X11 window or Wayland surface.

[jdm]

Both are possible—https://github.com/servo/servo/blob/main/components/servo/examples/winit_minimal.rs is an example of rendering directly to a winit window, but the main demo binary renders into an egui canvas with other UI elements present.