Joda's Instant corresponds to `std::time::SystemTime` in Rust. It was never intentional (source: I designed Chrono and it existed before `std::time`), but currently Chrono fills the calendar date and time while the standard library fills the monotonic and wall-clock timestamps.

To be honest, I think JSR-310 is not correct in every regard and its implementation of every ISO 8601 format is a mistake. I even started out Chrono without referring to JSR-310 (because I have designed other date and time libraries in the past). But it is much better than, say, Python datetime to which is being compared.