applyMirror

Applies mirror to this node, so the mirror belongs to it - which is what lets MirrorState.report answer a change inside the event that made it rather than from an event of its own.

declare states it for the declaration it settles, so a component built the usual way needs nothing here. State it directly where a component settles a mirror some other way - applying two declarations the widget resolves together, or reading back a property no declaration is written through. A mirror that reports without it fails at the first change.

Runs once, on the pass that creates the node: the composition a node stands in is the same for its whole life.

Parameters