EventAvail
EventAvail Get an event without removing it from the queue
#include <Events.h> Event Manager
Boolean EventAvail( eventMask, theEvent );
short eventMask ; bit flags for events; 0xFFFF is all events
EventRecord *theEvent ; receives the 16-byte event record
returns Is one of those events in the queue?
EventAvail is identical to GetNextEvent except that it does not remove the
event from the event queue. This lets you check for the occurrence of a
specific event (or any event) but leaves it in the queue for later processing.
eventMask is a 16-bit binary mask describing which events to include or
exclude. Use eventMask=everyEvent ( defined in Events.h as 0xFFFF)
to include all events. See Event Mask for the layout.
Some events (e.g., keyUp events) may never make it into the
event queue. See SetEventMask.
theEvent is the address of a 16-byte EventRecord. Upon return, it is filled
with an event description. See GetNextEvent or WaitNextEvent.
Returns: a Boolean value; it is the return value from an internal call to
SystemEvent and will be one of:
FALSE This is a DA or System or null event. Ignore it.
TRUE This event is intended for you. Examine and respond.

Notes: In a busy system, it is possible that an event read via this call will be
discarded before it can be processed. The Event Manager usually keeps
only 20 events, scrapping the oldest unread events to make room for new
ones.