Check whether ITfFunctionProvider is still supported in Windows 11 Microsoft IMEs #2
Description
This is probably a very Windows 8-specific feature, coupled with ITfFnSearchCandidateProvider and ITfIntegratableCandidateListUIElement.
It can be used to integrate candidate list to the app's UI. But since Windows 10 deleted charms bar (and GitHub search shows no real use), I believe it's not a real thing anymore.