https://w3c.github.io/webdriver-bidi/#command-browsingContext-getTree Required by the `top_context` fixture, used in many BiDi tests in WPT repository: https://github.com/web-platform-tests/wpt/blob/master/webdriver/tests/support/fixtures.py#L484 ``` @pytest_asyncio.fixture async def top_context(bidi_session): contexts = await bidi_session.browsing_context.get_tree() return contexts[0] ``` In a nutshell: - If the `parent` argument is null, return a list with all top-level navigables - If `parent` is not null, run the "get navigable info" algorithm[1], to traverse the navigable tree under `parent`, collecting information. [1] https://w3c.github.io/webdriver-bidi/#get-the-navigable-info