Class string

example/json.cpp:74–74

    bp::rule<class null, value> const null = "null";
    bp::rule<class string, std::string> const string = "string";
    bp::rule<class number, double> const number = "number";
    bp::rule<class object_element, boost::parser::tuple<std::string, value>> const
        object_element = "object-element";