code: public void writeDocument(OutputStream os, MediaType mt, Document document) {
          ProvFormat format = mimeTypeRevMap.get(mt.toString());
          writeDocument(os, format, document);
      }
docs: Write a {@link Document} to output stream, according to specified Internet Media Type
  @param os an {@link OutputStream} to write the Document to
  @param mt a {@link MediaType}
  @param document a {@link Document} to serialize