Returns the column's data format. Valid formats are:
- text-single -> single line or word of text
- text-private -> instead of showing the user what they typed, you show ***** to
protect it
- text-multi -> multiple lines of text entry
- list-single -> given a list of choices, pick one
- list-multi -> given a list of choices, pick one or more
- boolean -> 0 or 1, true or false, yes or no. Default value is 0
- fixed -> fixed for putting in text to show sections, or just advertise your web
site in the middle of the form
- hidden -> is not given to the user at all, but returned with the questionnaire
- jid-single -> Jabber ID - choosing a JID from your roster, and entering one based
on the rules for a JID.
- jid-multi -> multiple entries for JIDs