It looks like the "one of" operator maps to "iregex" under the hood. Does this mean that the value should be a regular expression? The confusion hit for me when I went to input the value, and it provided an autocomplete field which I was only allowed to select one of (I expected to see an interface that would allow me to choose multiple values). So, should the value of this operator type be a rege

It should be implemented as settable property. Note, that cache should be cleared after the setting the new value.