code: @Override
    public NonBlockingStringWriter append (final CharSequence aCS, final int nStart, final int nEnd)
    {
      final CharSequence cs = (aCS == null ? "null" : aCS);
      write (cs.subSequence (nStart, nEnd).toString ());
      return this;
    }
docs: Appends a subsequence of the specified character sequence to this writer.
  <p>
  An invocation of this method of the form <tt>out.append(csq, start,
  end)</tt> when <tt>csq</tt> is not <tt>null</tt>, behaves in exactly the same
  way as the invocation
  
  <pre>
  out.write (csq.subSequence (start, end).toString ())
  </pre>
  
  @param aCS
  The character sequence from which a subsequence will be appended. If
  <tt>csq</tt> is <tt>null</tt>, then characters will be appended as if
  <tt>csq</tt> contained the four characters <tt>"null"</tt>.
  @param nStart
  The index of the first character in the subsequence
  @param nEnd
  The index of the character following the last character in the
  subsequence
  @return This writer
  @throws IndexOutOfBoundsException
  If <tt>start</tt> or <tt>end</tt> are negative, <tt>start</tt> is
  greater than <tt>end</tt>, or <tt>end</tt> is greater than
  <tt>csq.length()</tt>