I'd like to be able to trigger the validations for a field, including relevant entity constraints, on a change (or equivalent) event for the field using AJAX. But I cannot figure out how to make that happen. It looks like the validation code is being called, but validations are disabled in form state (limit_validation_errors is set to ). I can hack that but I assume it's doing that for a reason.
I would have thought that this is a pretty common thing to do but either no or I am failing at picking the right search keywords.