Derive Macro Event 

#[derive(Event)]
{
    // Attributes available to this derive:
    #[topic]
    #[event_spec]
}

Derive event encoding, signature and spec metadata.

#[event_spec(wire_crate = "...")] pins the package label used in the signature hash, for protocol-defined events whose wire identity must survive a package rename. Spec names still use the declaring package. Combine with export to retain the event’s spec without an interface emits(...) entry.