[#before_4_2]
['Definitions before section 4.2.]

  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/int_.hpp>

  #include <boost/metaparse/build_parser.hpp>

  using namespace boost::metaparse;

  using exp_parser1 = build_parser<int_>;
  #include <boost/metaparse/entire_input.hpp>

  using exp_parser2 = build_parser<entire_input<int_>>;
  #include <boost/metaparse/token.hpp>

  using exp_parser3 = build_parser<entire_input<token<int_>>>;
  #include <boost/metaparse/lit_c.hpp>

  #include <boost/metaparse/sequence.hpp>

  using exp_parser4 = build_parser<sequence<token<int_>, token<lit_c<'+'>>, token<int_>>>;

  #include <metashell/formatter.hpp>
  
  using int_token = token<int_>;

  using plus_token = token<lit_c<'+'>>;

  using exp_parser5 = build_parser<sequence<int_token, plus_token, int_token>>;

