Limit AjaxSelectFieldWidget to one selectable value

I've added an extra field via a behavior, according to the subject field of the categorization behavior, to a type.

How would I limit the selection to just one value?
I've tried pattern_options 'maximumSelectionLength': 1 and 'selectionAdapter': 'SingleSelection' as widget directive, but no success. (and yes, the options are visible in data-pat-select2)

Any idea?

@agitator Did you ever figure out how to limit the Widget to selecting one value? I'm running into exactly the same issue.

To answer the question myself: it might not have worked for @agitator right away because the 'adapter' name has changed in select2 4, but we are probably still using select2 < 4 in mockup:

                  pattern_options={'maximumSelectionSize': '1'}

works. (in select2 4 you should use {'maximumSelectionLength': '1',} if the pattern is upgraded).