docs: def _set_element_text(self, prop_name, value):
          """Set string value of *name* property to *value*."""
          if not is_string(value):
              value = str(value)
  
          if len(value) > 255:
              tmpl = (
                  "exceeded 255 char limit for property, got:\n\n'%s'"
              )
              raise ValueError(tmpl % value)
          element = self._get_or_add(prop_name)
          element.text = value