template<class charT>
  unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'));
template<class charT, class traits, class Allocator>
  unspecified quoted(const basic_string<charT, traits, Allocator>& s,
                     charT delim = charT('"'), charT escape = charT('\\'));
template<class charT, class traits>
  unspecified quoted(basic_string_view<charT, traits> s,
                     charT delim = charT('"'), charT escape = charT('\\'));
template<class charT, class traits, class Allocator>
  unspecified quoted(basic_string<charT, traits, Allocator>& s,
                     charT delim = charT('"'), charT escape = charT('\\'));