Derive Macro EntityEvent 

#[derive(EntityEvent)]
{
    // Attributes available to this derive:
    #[entity_event]
    #[event_target]
}

Cheat sheet for derive syntax, see full explanation on EntityEvent trait docs.

#[derive(EntityEvent)]
/// Enable propagation, which defaults to using the ChildOf component
#[entity_event(propagate)]
/// Enable propagation using the given Traversal implementation
#[entity_event(propagate = &'static ChildOf)]
/// Always propagate
#[entity_event(auto_propagate)]
struct MyEvent;