docs: def get_witness(self, work, siglum, text_class=WitnessText):
          """Returns a `WitnessText` representing the file associated with
          `work` and `siglum`.
  
          Combined, `work` and `siglum` form the basis of a filename for
          retrieving the text.
  
          :param work: name of work
          :type work: `str`
          :param siglum: siglum of witness
          :type siglum: `str`
          :rtype: `WitnessText`
  
          """
          filename = os.path.join(work, siglum + '.txt')
          self._logger.debug('Creating WitnessText object from {}'.format(
              filename))
          with open(os.path.join(self._path, filename), encoding='utf-8') \
                  as fh:
              content = fh.read()
          return text_class(work, siglum, content, self._tokenizer)