I have a term reference field in the format of checkboxes. However, I'd like to disallow certain combinations of checkboxes. The options are:
None Food Drinks
The "None" option is not the default none, but a taxonomy term that is actually stored in the database. I'm wondering how to allow two selections, but to disallow the selection of both "Food" and "None", or "Drinks" and "None", since in practice that really doesn't make any sense. Any suggestions?