public function add_help_tab( $id, $title ) {

    $current_screen = get_current_screen();

    if ( null === $current_screen ) {
      return;
    }

    $current_screen->add_help_tab(
      [
        'id'       => $this->pagehook . '-' . $id,
        'title'    => $title,
        'content'  => '',
        'callback' => [ $this, 'help_content' ],
      ]
    );

  }