void set_inconsistent(bool setting
If the user has selected a range of elements (such as some text or
spreadsheet cells) that are affected by a toggle button, and the current
values in that range are inconsistent, you may want to display the toggle
in an "in between" state. This function turns on "in between" display.
Normally you would turn off the inconsistent state again if the user
toggles the toggle button. This has to be done manually,
set_inconsistent() only affects visual appearance, it doesn't affect the
semantics of the button.