int square(int num) {
    return ctre::starts_with<R"([\x80-\xBF])">("abc");
}

<source>: In instantiation of 'static constexpr bool ctre::char_range<A, B>::match_char(CharT, const ctre::flags&) [with CharT = char; auto A = 128; auto B = 191]':
<source>:1609:30:   required from here
 1609 |                 return (Content::match_char(value, f) || ... || false);
      |                         ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
<source>:5984:47:   in 'constexpr' expansion of 'ctre::starts_with<ctll::fixed_string<11>{char32_t [11]{91, 92, 120, 56, 48, 45, 92, 120, 66, 70, 93}, 11, true}>.ctre::regular_expression<ctre::set<ctre::char_range<128, 191> >, ctre::starts_with_method, ctll::list<ctre::singleline> >::operator()<const char (&)[4]>("abc")'
<source>:5651:14:   in 'constexpr' expansion of 'ctre::regular_expression<ctre::set<ctre::char_range<128, 191> >, ctre::starts_with_method, ctll::list<ctre::singleline> >::exec(((const char*)std::forward<const char (&)[4]>((* & args#0))))'
<source>:5623:41:   in 'constexpr' expansion of 'ctre::starts_with_method::exec<ctll::list<ctre::singleline> >(s, (ctre::zero_terminated_string_end_iterator(), ctre::zero_terminated_string_end_iterator()), (ctre::set<ctre::char_range<128, 191> >(), ctre::set<ctre::char_range<128, 191> >()))'
<source>:5559:40:   in 'constexpr' expansion of 'ctre::starts_with_method::exec<ctll::list<ctre::singleline>, void, ctre::set<ctre::char_range<128, 191> >, const char*, ctre::zero_terminated_string_end_iterator>(begin, begin, (end, ctre::zero_terminated_string_end_iterator()), (ctre::set<ctre::char_range<128, 191> >(), ctre::set<ctre::char_range<128, 191> >()))'
<source>:5555:18:   in 'constexpr' expansion of 'ctre::evaluate<regex_results<const char*>, const char*, const char*, zero_terminated_string_end_iterator, set<char_range<128, 191> >, end_mark, accept>(orig_begin, begin, (end, ctre::zero_terminated_string_end_iterator()), ctre::flags((ctll::list<ctre::singleline>(), ctll::list<ctre::singleline>())), ctre::regex_results<const char*>(), (ctll::list<ctre::start_mark, ctre::set<ctre::char_range<128, 191> >, ctre::end_mark, ctre::accept>(), ctll::list<ctre::start_mark, ctre::set<ctre::char_range<128, 191> >, ctre::end_mark, ctre::accept>()))'
<source>:4607:17:   in 'constexpr' expansion of 'ctre::evaluate<regex_results<const char*>, const char*, const char*, zero_terminated_string_end_iterator, set<char_range<128, 191> >, end_mark, accept>(((const char*)begin), current, (last, const ctre::zero_terminated_string_end_iterator()), (* & f), (*(const ctre::regex_results<const char*>*)(& captures.ctre::regex_results<const char*>::set_start_mark(current))), (ctll::list<ctre::set<ctre::char_range<128, 191> >, ctre::end_mark, ctre::accept>(), ctll::list<ctre::set<ctre::char_range<128, 191> >, ctre::end_mark, ctre::accept>()))'
<source>:4631:32:   in 'constexpr' expansion of 'ctre::set<ctre::char_range<128, 191> >::match_char<char>(((int)((char)(* current))), (* & f))'
<source>:1636:31: warning: comparison of integer expressions of different signedness: 'char' and 'char32_t' [-Wsign-compare]
 1636 |                 return (value >= A) && (value <= B);
      |                        ~~~~~~~^~~~~
<source>:1636:47: warning: comparison of integer expressions of different signedness: 'char' and 'char32_t' [-Wsign-compare]
 1636 |                 return (value >= A) && (value <= B);
      |                                        ~~~~~~~^~~~~