public function register_setting( $setting_name, $setting, $panel ) {

    $defaults = [
      'type' => 'option',
    ];

    $setting = wp_parse_args( $setting, $defaults );

    $setting_name = isset( $panel['settings_field'] ) ? sprintf( '%s[%s]', $panel['settings_field'], $setting_name ) : $setting_name;

    $this->wp_customize->add_setting(
      $setting_name,
      $setting
    );

  }