class Tag {

  public final void tag(I input, ScopedSpan span) {
    if (input == null) throw new NullPointerException("input == null");
    if (span == null) throw new NullPointerException("span == null");
    if (span.isNoop()) return;
    tag(span, input, span.context());
  }

  protected  Tag(String key);

}