code: def getDocFactory(self, fragmentName, default=None):
          
          themes = self._preferredThemes()
          for t in themes:
              fact = t.getDocFactory(fragmentName, None)
              if fact is not None:
                  return fact
          return default
docs: Retrieve a Nevow document factory for the given name.
  
          @param fragmentName: a short string that names a fragment template.
  
          @param default: value to be returned if the named template is not
          found.