It is a directory for api-xml-adjuster build-only tool, as well as a work directory to regenerate src/Mono.Android/Profiles/api-*.xml.in.

Generating those api-*.xml.in takes too much time to download the docs archives (which are not always provided by Google, by the way), scrape all those DroidDoc HTMLs and then re-parsed to resolve inheritance hierarchy to generate correct (backward-compatible) API description XML.

It should happen only once in a while (every time Google publishes a new API Level with docs).

(Well, I'm not very honest above: it should be built every time with our latest class-parse and api-xml-adjuster so that those toolchains don't trigger regressions that can cause Mono.Android API breakage. But as I stated above, it takes too much time anyways...)

Because you don't want to clean up and download them every time you run MSBuild /t:Clean.

It had existed as such, and it's not part of the build, no need to be built on Windows so far.

Google publishes the docs SDK component only against the stable API, which means that preview API types are not included. That makes our parameter names retrieval impossible for the preview API.

To workaround the issue, we create corresponding API docs zip archive from developer.android.com using the following tool: https://github.com/xamarin/components/tree/master/AndroidDocUtil