@Override
    public void startPrefixMapping(final String prefix, final String uri) throws SAXException {
        if (handler != null) {
            handler.startPrefixMapping(prefix, uri);
        } else {
            super.startPrefixMapping(prefix, uri);
        }
    }
Buffers a startPrefixMapping event if buffer is set to true.

@param prefix the Namespace prefix being declared. An empty string is used
              for the default element namespace, which has no prefix.
@param uri    the Namespace URI the prefix is mapped to
@throws SAXException Not thrown.
@see stroom.pipeline.filter.AbstractXMLFilter#startPrefixMapping(java.lang.String,
java.lang.String)
stroom-pipeline/src/main/java/stroom/pipeline/filter/BufferFilter.java