Inspecting the `Right Alt` key messages using `Microsoft Spy++` returns the following:
Code:
WM_KEYDOWN nVirtKey:VK_CONTROL 
WM_KEYDOWN nVirtKey:VK_MENU
WM_SYSKEYUP nVirtKey:VK_CONTROL
WM_KEYUP nVirtKey:VK_MENU
Why does the key generate 2 messages `VK_CONTROL` and `VK_MENU`? Why is the type of `VK_CONTROL` SYS (system) while `VK_MENU` non-system?