code: public void onProcessingInstruction (@Nonnull final String sTarget, @Nullable final String sData)
    {
      _append (PI_START)._append (sTarget);
      if (StringHelper.hasText (sData))
        _append (' ')._append (sData);
      _append (PI_END);
      newLine ();
    }
docs: On processing instruction
  
  @param sTarget
  The target
  @param sData
  The data (attributes as a string)