Gtk.TextBuffer.prototype.add_selection_clipboard

function add_selection_clipboard(clipboard:Gtk.Clipboard):void {
    // Gjs wrapper for gtk_text_buffer_add_selection_clipboard()
}

Adds clipboard to the list of clipboards in which the selection contents of buffer are available. In most cases, clipboard will be the Gtk.Clipboard of type %GDK_SELECTION_PRIMARY for a view of buffer.