code: public Content getTagletOutput(Element holder, DocTree tag, TagletWriter writer) {
          return writer.getDocRootOutput();
      }
docs: Given a <code>Doc</code> object, check if it holds any tags of
  this type.  If it does, return the string representing the output.
  If it does not, return null.
  @param holder
  @param tag a tag representing the custom tag.
  @param writer a {@link TagletWriter} Taglet writer.
  @return the string representation of this <code>Tag</code>.