-spec casefold(unicode:chardata()) -> maybe_improper_list(gc(), unicode:chardata()).

-spec cp(String :: unicode:chardata()) -> maybe_improper_list() | {error, unicode:chardata()}.

-spec gc(String :: unicode:chardata()) -> maybe_improper_list() | {error, unicode:chardata()}.

-spec get_case(char()) -> #{fold := gc(), lower := gc(), title := gc(), upper := gc()}.

-spec is_whitespace(gc()) -> boolean().

-spec is_wide(gc()) -> boolean().

-spec lookup(char()) ->
          #{canon := [{byte(), char()}],
            ccc := byte(),
            compat := [] | {atom(), [{byte(), char()}]},
            category := {atom(), atom()}}.

-spec lowercase(unicode:chardata()) -> maybe_improper_list(gc(), unicode:chardata()).

-spec nfc(unicode:chardata()) ->
       maybe_improper_list(gc(), unicode:chardata()) | {error, unicode:chardata()}.

-spec nfd(unicode:chardata()) ->
       maybe_improper_list(gc(), unicode:chardata()) | {error, unicode:chardata()}.

-spec nfkc(unicode:chardata()) ->
        maybe_improper_list(gc(), unicode:chardata()) | {error, unicode:chardata()}.

-spec nfkd(unicode:chardata()) ->
        maybe_improper_list(gc(), unicode:chardata()) | {error, unicode:chardata()}.

-spec titlecase(unicode:chardata()) -> maybe_improper_list(gc(), unicode:chardata()).

-spec uppercase(unicode:chardata()) -> maybe_improper_list(gc(), unicode:chardata()).

-spec whitespace() -> [gc()].