A 4-byte message-dependent parameter structure.

typedef VOID *MPARAM;

Certain elements of information, placed into the parameters of a message, have data types that do not use all four bytes of this data type. The rules governing these cases are:

BOOL

The value is contained in the low word and the high word is 0.
SHORT
The value is contained in the low word and its sign is extended into the high word.
USHORT
The value is contained in the low word and the high word is 0.
NULL
The entire four bytes are 0.

The structure of this data type depends on the message. For details, see the description of the particular message.

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