WM_MENUSELECT

  This message is sent to the window who owns the menubar when a menubar
item or a pulldown menu item is highlighted. This gives the application the
opportunity to perform an action like printing some help text whenever the
highlight moves over a menu item. It is also sent when a menu is being
dismissed, This gives the application the chance to remove any help
messages associated with the menu.

Parameters
  wParam is the identifier of the menu item. It is 0 if the menu is being
   dismissed.
  lParam is not used.