code: public final Mono<T> tag(String key, String value) {
  		return MonoName.createOrAppend(this, key, value);
  	}
docs: Tag this mono with a key/value pair. These can be retrieved as a {@link Set} of
  all tags throughout the publisher chain by using {@link Scannable#tags()} (as
  traversed
  by {@link Scannable#parents()}).
  
  @param key a tag key
  @param value a tag value
  @return the same sequence, but bearing tags