code: def _on_sphinx_thread_error_msg(self, error_msg):
          
          self._sphinx_thread.wait()
          self.plain_text_action.setChecked(True)
          sphinx_ver = programs.get_module_version('sphinx')
          QMessageBox.critical(self,
                      _('Help'),
                      _("The following error occured when calling "
                        "<b>Sphinx %s</b>. <br>Incompatible Sphinx "
                        "version or doc string decoding failed."
                        "<br><br>Error message:<br>%s"
                        ) % (sphinx_ver, error_msg))
docs: Display error message on Sphinx rich text failure