code: HtmlTag add(Object... contents) {
          for (Object content : contents) {
              this.contents.add(content);
          }
          return this;
      }
docs: Add the contents.
  <p>
  {@link Object#toString()} is used when generating the string representation of the tag. The value is escaped using {@link Strings#escape(String)} for
  instances which are neither {@link HtmlTag} nor {@link SafeString}.
  
  @param content
  @return self