int = GetClipboardSequenceNumber()
The GetClipboardSequenceNumber function returns the clipboard sequence number for the current window station.
[This is preliminary documentation and subject to change.]
The system keeps a 32-bit serial number for the clipboard for each window
station. This number is incremented whenever the contents of the
clipboard change or the clipboard is emptied. You can track this value to
determine whether the clipboard contents have changed and optimize
creating DataObjects. If clipboard rendering is delayed, the sequence
number is not incremented until the changes are rendered.