ctldata (PVOID)
This points to a Control-Data data structure initialized with the data provided in the parameter of the WinCreateWindow function. This pointer is also contained in the pCREATE parameter.
This parameter MUST be a pointer rather than a long.
The first 2 bytes in the data referenced by this pointer should be the total size of the data referenced by the pointer, (for example, see the ENTRYFDATA or the FRAMECDATA structure). PM requires this information to enable it to ensure that the referenced data is accessible to both 16-bit and 32-bit code.