Inside Macintosh: Macintosh Toolbox Essentials
You use posting option enumerators with PostHighLevelEvent (PostHighLevelEvent) to indicate how you are specifying the receiver of the high-level event and how you want the event to be delivered.
enum { /* posting option enumerators */
receiverIDMask = 0x0000F000, /* mask for receiver ID bits */
receiverIDisPSN = 0x00008000, /* ID is process serial number */
receiverIDisSignature = 0x00007000, /* ID is creator signature */
receiverIDisSessionID = 0x00006000, /* ID is PPC session reference
/* number */
receiverIDisTargetID = 0x00005000, /* ID is port name and location name */
systemOptionsMask = 0x00000F00, /* system options */
nReturnReceipt = 0x00000200, /* return receipt requested */
priorityMask = 0x000000FF, /* priority */
nAttnMsg = 0x00000001 /* give this message priority */
/* class and ID values for return receipt */
HighLevelEventMsgClass = 'jaym', /* high-level events message class */
rtrnReceiptMsgID = 'rtrn', /* return receipt message ID */
/* modifiers values in return receipt */
msgWasPartiallyAccepted = 2, /* message was partially accepted */
msgWasFullyAccepted = 1, /* message was fully accepted */
msgWasNotAccepted = 0 /* message was not accepted */
};