Description:

Asks to keep RForm below (if set to true), so that it stays on bottom.
Note that you shouldn't assume the RForm is definitely below afterward, because other entities (e.g. the user or window manager) could not keep it below, and not all window managers support keeping windows below. But normally the window will end kept below. Just don't write code that crashes if not.
It's permitted to call this function before showing a window, in which case the window will be kept below when it appears onscreen initially.