for (final Map.Entry<String, String> entry : fieldRuleMap.entrySet()) {
            final String path = entry.getValue();
            try {
                final XPathEvaluationResult<?> xObj = getXPathAPI().eval(document, path);
                switch (xObj.type()) {
                case BOOLEAN:
                    final Boolean b = (Boolean) xObj.value();

                return namespace;
            }
            return "http://crawler.codelibs.org/namespace/" + prefix;
        }

        @Override
        public Iterator<String> getPrefixes(final String val) {
            return null; // not used
        }

        @Override
        public String getPrefix(final String uri) {
            return null; // not used
        }
    }