Method on_replacement_field

extlibs/fmt/include/fmt/format.h:3168–3172

  void on_arg_id(basic_string_view<Char> id) { arg = context.arg(id); }

  void on_replacement_field(const Char* p) {
    advance_to(parse_context, p);
    context.advance_to(
        visit_format_arg(ArgFormatter(context, &parse_context), arg));
  }

  const Char* on_format_specs(const Char* begin, const Char* end) {
    advance_to(parse_context, begin);