I have two fields, a select list of checkboxes and a taxonomy term reference. I would like the taxonomy term reference to be optional unless one of the checkboxes has a certain value, in which case a value must be entered into the taxonomy term reference field.
Is there a module that can accomplish this? I tried the Field Validation module but I couldn't find a way to configure it for this use case. Custom code is fine too if you could point me in the right direction.