Data sources for user-supplied data.
DataGet is GET data,
DataPost is POST data.
DataRequest is a combination of the two (except that if any keys that occur in both sources, only the values from POST will be available for these sources).
DataCookie retrieves cookies, and
DataNone is always empty.
DataRequest should only be used where the application is genuinely expected to receive user-supplied data by both request methods (for example, a search form).