Gtk.Widget.prototype.set_parent

function set_parent(parent:Gtk.Widget):void {
    // Gjs wrapper for gtk_widget_set_parent()
}

This function is useful only when implementing subclasses of Gtk.Container. Sets the container as the parent of widget, and takes care of some details such as updating the state and style of the child to reflect its new location. The opposite function is Gtk.unparent.