Applications can store custom data using ObjUserData. ObjUserData contains a pointer to a user buffer with a length specified by ObjUserDataLength.
hobj is the ID of the object. You should not use IEV_NEXT_INSERTED_OBJECT (-1) or IEV_PREVIOUS_INSERTED_OBJECT (-2) for this property.
Note: The loading, saving and clipboard methods save this field by allocating a buffer when needed. When the object is destroyed the memory used by ObjUserData will be freed (if it has not been reset to nil).