code: @Override
      public void startDocument() throws IOException
      {
          // JSF 2.2 section 2.2.6.1 Render Response Partial Processing
          // use writePreamble(...)
          //_wrapped.write ("<?xml version=\"1.0\" encoding=\"utf-8\"?>");
          
          _wrapped.startElement ("partial-response", null);
          
          // If by some reason the response has been reset, and the same
          // PartialResponseWriter is used, it is necessary to ensure any 
          // variable is initialized in a consistent state. To do that,
          // the best point is when the document is started.
          hasChanges = false;
          insertType = null;
      }
docs: {@inheritDoc}