[#before_4]
['Definitions before section 4.]

  #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_>>>;

