code: public void addAttribute(String alias, AttributeKey<?> attrKey, Function<?, String> stringifier) {
          ensureNotStarted();
          builder.addAttribute(alias, attrKey, stringifier);
      }
docs: Adds the specified {@link AttributeKey} to the export list.
  
  @param alias the alias of the attribute to export
  @param attrKey the key of the attribute to export
  @param stringifier the {@link Function} that converts the attribute value into a {@link String}