namespace boost {
  namespace text {
    enum grapheme_property;
    grapheme_property grapheme_prop(uint32_t);
    namespace v1 {
      template<code_point_iter I, std::sentinel_for< I > S> 
        I prev_grapheme_break(I, I, S);
      template<code_point_iter I, std::sentinel_for< I > S> 
        I next_grapheme_break(I, S);
      template<code_point_range R> 
        std::ranges::borrowed_iterator_t< R > 
        prev_grapheme_break(R &&, std::ranges::iterator_t< R >);
      template<code_point_range R> 
        std::ranges::borrowed_iterator_t< R > 
        next_grapheme_break(R &&, std::ranges::iterator_t< R >);
      template<code_point_iter I, std::sentinel_for< I > S> 
        bool at_grapheme_break(I, I, S);
      template<code_point_range R> 
        bool at_grapheme_break(R &&, std::ranges::iterator_t< R >);
    }
  }
}