DFHMAC-ALLPARMS is used by the service requester to pass the contents of the DFHMAH header to the stub program.
You can also include the application data in this container, or pass the application data in the DFHMAC-USERDATA container. If you include the application data in this container, you can code it in XML and optionally the DFHMAH header.
If the DFHMAH header and the application data is in XML, then the length of the container is limited to 32,760 bytes. If the message header and application data are not in XML, the container can be up to, but not equal to, 16MB in length.