code: def get_word_file(self, mmax_base_file):
          
          return os.path.join(self.mmax_project.paths['project_path'],
                              self.mmax_project.paths['basedata'],
                              etree.parse(mmax_base_file).find('//words').text)
docs: parses an MMAX base file (``*.mmax``) and returns the path
          to the corresponding ``_words.xml`` file (which contains
          the tokens of the document).