gdk:toplevel-modal (object)

object -- a gdk:toplevel object
modal -- true if the surface is modal, false otherwise

The accessor for the modal slot of the gdk:toplevel class gets or sets whether the toplevel is modal. The application can use this hint to tell the window manager that a certain surface has modal behaviour. The window manager can use this information to handle modal surfaces in a special way.

You should only use this on surfaces for which you have previously called the gdk:toplevel-transient-for function.