Where can find Tracer in the code?

[kingctan]

back-link: ch08/index.html#simple-simulation

Emitter {
        id: emitter
        anchors.centerIn: parent
        width: 160; height: 80
        system: particleSystem
        emitRate: 10
        lifeSpan: 1000
        lifeSpanVariation: 500
        size: 16
        endSize: 32
        Tracer { color: 'green' }
    }