FormWindBegin() creates a modal window formular that is a
form displayed in a modal window. A modal window disables the
user interaction of the application. It is very similar to the
classic formular except the AES is not stopped. The events of
the formular are handled by FormWindDo(). The formular is closed
with FormWindEnd().
The user WinDom variable windom.mform.widget defines the widgets
of the window.