MIDL2223
The documentation lists this name without a value.
Documented in Win32
[allocate] is illegal on either the transmitted or presented type for [transmit_as], [represent_as], [wire_marshal], or [user_marshal] The [ transmit_as ] and [ allocate ] attributes cannot both be applied to the same type. The [ transmit_as ] attribute distinguishes between presented and transmitted types, while the [ allocate ] attribute assumes that the presented type is the same as the transmitted type.