Croner has a table for the syntax supported by it and saffron [1], you can compare it with the one cronexpr supported.

[1] https://github.com/hexagon/croner-rust?tab=readme-ov-file#wh...

As supported in [2],

> There are several good candidates like croner and saffron, but they are not suitable for my use case. Both of them do not support defining timezone in the expression which is essential to my use case. Although croner support specific timezone later when matching, the user experience is quite different. Also, the syntax that croner or saffron supports is subtly different from my demand. > > Other libraries are unmaintained or immature to use. > > Last, most candidates using chrono to processing datetime, while I’d prefer to extend the jiff ecosystem.

[2] https://docs.rs/cronexpr/latest/cronexpr/#why-do-you-create-...