Dispatch and Precedence

Handlers bound on NavLayer take precedence over handlers bound on Layer, which take precedence over handlers bound on Mercury.

#[derive(Bind)] emits one dispatch per node, and they chain through ControlFlow:

fn dispatch<'a>(
    path: NavLayerPath<'a>,
    event: &MercuryEvent,
) -> ControlFlow<Vec<MercuryEffect>, NavLayerPath<'a>>

A node descends into its active child before it looks at its own bindings, so the walk goes leafward first and unwinds rootward. Break carries the handler's output straight out, past every node still waiting on the way back up. Continue carries the path back instead, and the parent recovers its own path from it with into_parent and takes its turn. When the root hands back a Continue, bind::dispatch turns it into None, which is what state.handle returns for an event nothing bound.

Inside one node the bindings are tried in the order they are written in #[bind(..)], top to bottom, and the first whose trigger matches wins. So "first" is written order within a node and depth between nodes, and exactly one handler runs per event.

Narrowing the event

Dispatch narrows the event to &Self::Event with a TryFrom before it asks a trigger whether it matches. A key binding never sees a tab event: the narrowing fails and the binding is skipped.