@Override
    public CharBufferWriter append(final CharSequence csq, final int start, final int end) {
        final CharSequence cs = (csq == null ? "null" : csq);
        write(cs.subSequence(start, end).toString());
        return this;
    }
Appends a subsequence of the specified character sequence to this writer.
<p>
<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
<p>
<pre>
out.write(csq.subSequence(start, end).toString())
</pre>

@param csq   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 start The index of the first character in the subsequence
@param end   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>
@since 1.5
stroom-pipeline/src/main/java/stroom/pipeline/writer/CharBufferWriter.java