code: public static synchronized void setStderr(OutputStream os)
    {
      if (_stderrStream == null) {
        initStderr();
      }
  
      if (os == _systemErr || os == _systemOut) {
        return;
      }
  
      if (os instanceof WriteStream) {
        WriteStream out = (WriteStream) os;
  
        /*
        if (out.getSource() == StdoutStream.create()
            || out.getSource() == StderrStream.create()) {
          return;
        }
        */
      }
  
      _stderrStream.setStream(os);
    }
docs: Sets path as the backing stream for System.err