code: public void flush(char[] buf, int upUntil)
          throws XMLStreamException
      {
          if (mFlattenStart < upUntil) {
              if (mIsFlattening > 0) {
                  try {
                      mWriter.write(buf, mFlattenStart, upUntil - mFlattenStart);
                  } catch (IOException ioe) {
                      throw new WstxIOException(ioe);
                  }
              }
              mFlattenStart = upUntil;
          }
      }
docs: /*
  ////////////////////////////////////////////////
  Public API, output methods:
  ////////////////////////////////////////////////