Not selected with select_multiple

I have a select multiple field and I want to restrict selection of an option when any of the other options are selected. I tried using not selected like this not(selected(data(‘q1’), ‘A’)) but it did not work. Does ‘not selected’ work with select_multiple? What mistake am I making if it does? And if not, how can I restrict selection without the use of any js function? Thanks.

Ok, so it worked but not sure why it did with this change. All I did was use a numeric value as select_multiple choices. So, my not selected code became something like this:
not(selected(data(‘q1’), ‘1’))

Not sure why this fixed it, but glad it did!