I believe code should be consistent and use the existing `fmt::detail` namespace. There is a new namespace that was introduced in latest version `fmt_detail`. Would it be possible to use the existing `fmt::detail` or a `fmt::detail::chrono` namespace ? https://github.com/fmtlib/fmt/blob/41539c29f342e67abb925b946acab6d55d331b36/include/fmt/chrono.h#L25 For example when bundling `libfmt` under a custom namespace with a script, that is now an additional namespace that needs to be renamed