WM_NCXBUTTONUP top-level constant
int
const WM_NCXBUTTONUP
Posted when the user releases the first or second X button while the cursor is in the nonclient area of a window.
This message is posted to the window that contains the cursor. If a window has captured the mouse, this message is not posted.
To learn more, see learn.microsoft.com/windows/win32/inputdev/wm-ncxbuttonup.
Implementation
const WM_NCXBUTTONUP = 172;