Time time_attribute (std::string);
float float_attribute (std::string);
std::string string_attribute (std::string);
+ std::string optional_string_attribute (std::string);
int64_t int64_attribute (std::string);
int64_t optional_int64_attribute (std::string);
boost::optional<bool> optional_bool_attribute (std::string);
+ boost::optional<Color> optional_color_attribute (std::string);
std::string content ();