Providing DEVMODE Structure Additions
Your UI plug-in can add its own private members to the DEVMODEW structure, as illustrated in the following figure.
A UI plug-in can use these private DEVMODE members to store values associated with customized printer options. The plug-in makes these options available to the user by modifying a driver-supplied property sheet page or by adding new property sheet pages.
If your UI plug-in adds private DEVMODE members, the OEM_DMEXTRAHEADER structure must prefix the added members.
You are not required to add members to the DEVMODE structure, but if you do, your UI plug-in must implement the IPrintOemUI::DevMode method. This method's purpose, depending on input arguments, is to return the size of, initialize, convert, or validate the additional DEVMODE members.