Which regex should be entered to prevent users from saving invalid characters in the Table Editor?
These expressions need to be added to the table validation expression field directly. An alternative solution is to remove and re-add the entity, then restart application.
The table editor has a validation expression in its designer, so if a you add a validation expression off of the attributes in the data model, and the able editor has already been designed and the entity was already added to the table editor, the table will need to be rebuilt.