Summary
Finally, I found the related issue, setForeground() incorrectly flagged as requiring API 23 on ViewGroups extending Frame
Finally I found the related issue, setForeground() incorrectly flagged as requiring API 23 for ViewGroups extending FrameLayout.
Issue 189041: setForeground() incorrectly flagged as requiring API 23 (NewApi) for ViewGroups extending FrameLayout
If you are not extending FrameLayout, the documentation is wrong and API 23 is really required.
Issue 186273: View.setForeground wrong API level