UNIDRV - custom size

Question

I am working on creating a printer unidrv, and I want to allow users to set the paper size. I tried referring to Microsoft's website regarding this matter, but I am still unsure. Could you please assist me with how to proceed?

Here is my CUSTOMSIZE in GPD file

   *Option: CUSTOMSIZE{
      *Name: "CUSTOM SIZE"
      *MinSize: PAIR(2352, 3384)
      *MaxSize: PAIR(2352, 5534)
      *MaxPrintableWidth: 5534
      *MinLeftMargin: 0
      *TopMargin: 0
      *BottomMargin: 0
      *CenterPrintable?: FALSE
      *CursorOrigin: (0, 0)
      *PageProtectMem: 8192
      *Command : CustomPaperSize
      {
           *Order: DOC_SETUP.13
           *Cmd: ""
      }
   }

Thanks in advance!

It seems like I need to modify the GPD file and the CommandCallback function, but I'm not sure about it, and I don't know how to do it.