System modal dialogs are much the same as full application modal dialogs. But with system modal dialogs, the user must respond to the dialog before doing anything else in any application. Because an exclusive Xt grab is only effective within the application, any LESSTIF application needs additional help from the window manager to make a dialog system modal. Currently, only mwm (and thus lmwm) provides the help needed. If there is no suitable window manager present, the system modal dialog behaves like any full application modal dialog.
In the case of a system modal dialog the grab list looks like the one presented in figure .