code: def write_paula(docgraph, output_root_dir, human_readable=False):
      
      paula_document = PaulaDocument(docgraph, human_readable=human_readable)
      error_msg = ("Please specify an output directory.\nPaula documents consist"
                   " of multiple files, so we can't just pipe them to STDOUT.")
      assert isinstance(output_root_dir, str), error_msg
      document_dir = os.path.join(output_root_dir, paula_document.name)
      if not os.path.isdir(document_dir):
          create_dir(document_dir)
      for paula_id in paula_document.files:
          with open(os.path.join(document_dir, paula_id+'.xml'), 'w') as outfile:
              outfile.write(
                  paula_etree_to_string(paula_document.files[paula_id],
                                        paula_document.file2dtd[paula_id]))
docs: converts a DiscourseDocumentGraph into a set of PAULA XML files
      representing the same document.
  
      Parameters
      ----------
      docgraph : DiscourseDocumentGraph
          the document graph to be converted