Return the number of errors during parsing @ignore
protected function parserErrorCount($parser) {
$errorUri = librdf_new_uri($this->world, self::LIBRDF_PARSER_FEATURE_ERROR_COUNT);
$errorNode = librdf_parser_get_feature($parser, $errorUri);
$errorCount = librdf_node_get_literal_value($errorNode);
librdf_free_uri($errorUri);
return $errorCount;
}