Gtk.Button.new_with_mnemonic

function new_with_mnemonic(label:String):Gtk.Widget {
    // Gjs wrapper for gtk_button_new_with_mnemonic()
}

Creates a new Gtk.Button containing a label. If characters in label are preceded by an underscore, they are underlined. If you need a literal underscore character in a label, use '__' (two underscores). The first underlined character represents a keyboard accelerator called a mnemonic. Pressing Alt and that key activates the button.