Gtk.Label.prototype.set_pattern

function set_pattern(pattern:String):void {
    // Gjs wrapper for gtk_label_set_pattern()
}

The pattern of underlines you want under the existing text within the Gtk.Label widget. For example if the current text of the label says "FooBarBaz" passing a pattern of "___ ___" will underline "Foo" and "Baz" but not "Bar".