WM_MOUSELAST

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Shouldn't WM_MOUSELAST = 02Ah ?

Since it's not an actual message in itself, but rather a bracketing message, i.e. to group mouse messages, you search from MOUSEFIRST to MOUSELAST, WM_MOUSELAST needs to be updated to reflect that more mouse messages have been added (WM_MOUSEWHEEL specifically).  Updating the value should have no effect on older code or for use on previous versions of Windows that do not contain the new message, because it will never be found as a message, and therefore not cause any problems.