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A customisation point that queries the value of a property.
constexpr unspecified query = unspecified;
        The name query denotes a customization point object. The expression
        boost::asio::query(E, P) for some subexpressions E
        and P (with types T = decay_t<decltype(E)>
        and Prop = decay_t<decltype(P)>) is expression-equivalent
        to:
      
is_applicable_property_v<T, Prop> is not a well-formed
            constant expression with value true, boost::asio::query(E,
            P) is ill-formed.
          Prop::template static_query_v<T> if the
            expression Prop::template static_query_v<T> is a well-formed
            constant expression.
          (E).query(P) if the expression (E).query(P)
            is well-formed.
          query(E, P) if the expression query(E,
            P) is a valid expression with overload resolution performed in
            a context that does not include the declaration of the query
            customization point object.
          boost::asio::query(E, P) is ill-formed.
          
        Header: boost/asio/query.hpp
      
        Convenience header: boost/asio.hpp