DDF data is treated differently for a help and an online document. In the case of a help facility, the HM_QUERY_DDF_DATA message must be processed in the application's window procedure. Within the processing for this message, you can turn on the number specified in the res= attribute of the :ddf. tag to allow for different processing based on which IPF window with a :ddf. tag is currently being displayed.

Therefore, in the case of dynamic data formatting within help, it is not necessary to specify an application-controlled window or a separate DLL. However, this would also work if the application-controlled window used the HM_SET_OBJCOM_WINDOW message to explicitly identify the entry point specified in the dll=' ' and objectname=' ' attributes of the :acviewport. tag as the proper window procedure where the HM_QUERY_DDF_DATA message is processed.