View source for Template:AllowEmptyDescription

'''<u>Allow Empty</u>'''
:Because the values in a Combo Box [[Custom Field]] are restricted to the semi-colon delimited list in the '''Values''' field, the '''Allow Empty''' field has a slightly different behaviour than usual. It controls whether or not the record can be saved with the default value (which is the first value listed in the '''Values''' section):
:* If '''Allow Empty''' is checked, the record '''can''' be saved with the default value.
:* If '''Allow Empty''' is '''not''' checked, the record '''cannot''' be saved with the default value. In this way you can force the user to select a value different from the default value.
:* '''Important:''' Because the record cannot be saved with the default value, the first item listed in the '''Value''' section should be either a space followed by a semi-colon (if you want the field to start out blank) or an instruction to the user such as ''-----Select One-----; Please choose;'' or similar. You do not want an actual value as the first item, since the record can never be saved with the first value if '''Allow Empty''' is deselected.