WORD pascal PeekMessage(LPMSG lpMsg)

  This function checks the system message queue for a pending message.
If a message was found, it will not be removed from the message
queue. This message can be later read and dequeued by using
GetMessage(). Using PeekMessage() will allow you to perform background
processing while no messages are in the queue.

Parameters
  lpMsg is a pointer to a MSG structure.

Returns
  This function returns FALSE (0) if there is no message pending.
Otherwise, it returns the message field of the MSG structure. The
message structure is filled with the various message values, but the
message is not removed from the queue.