@Override
    public void characters(final char[] ch, final int start, final int length) throws SAXException {
        if (buffer) {
            events.add(new Characters(ch, start, length));
        } else {
            super.characters(ch, start, length);
        }
    }
Buffers a characters event if buffer is set to true.

@param ch     An array of characters.
@param start  The starting position in the array.
@param length The number of characters to use from the array.
@throws SAXException Not thrown.
@see stroom.pipeline.filter.AbstractXMLFilter#characters(char[],
int, int)
stroom-pipeline/src/test/java/stroom/pipeline/util/BufferFilter.java