Type Alias InputHandlerFn 

pub type InputHandlerFn = dyn Fn(InputHandlerInput<'_>) + Send + Sync;

A InputHandlerFn is a function that handles state changes for a component.

The rule of execution order is:

1. Children’s input handlers are executed earlier than parent’s.
2. Newer components’ input handlers are executed earlier than older ones.

Acutally, rule 2 includes rule 1, because a newer component is always a child of an older component :)