Описание тега systemmenu
In Microsoft Windows, the system menu is a popup menu that contains common window operations such as "Minimize" and "Close".
In Microsoft Windows, the system menu is a popup menu that contains common window operations such as "Minimize" and "Close". It can be opened by clicking on the icon in the upper-left corner, by pressing alt+space, or by right-clicking on the title bar.
An application can modify this menu (e.g. add a custom entry) with GetSystemMenu and related WinAPI functions.