def _read_stderr(self):
        """
        Reads the child process' stderr and process it.
        """
        output = self._decode(self._process.readAllStandardError().data())
        if self._formatter:
            self._formatter.append_message(output, output_format=OutputFormat.ErrorMessageFormat)
        else:
            self.insertPlainText(output)
Reads the child process' stderr and process it.