How to use renderOrder?

HTML

<script src="http://threejs.org/build/three.min.js"></script>
<script src="http://threejs.org/examples/js/controls/OrbitControls.js"></script>

CSS

body {
    background-color: #000;
    margin: 0px;
    overflow: hidden;
}

JavaScript

// Two Scenes with the Second One on Top
// Three.js r.69

var mesh1, mesh2, renderer, scene, camera;
var controls;

init();
animate();

function init() {

    // info
    info = document.createElement( 'div' );
    info.style.position = 'absolute';
    info.style.top = '30px';
    info.style.width = '100%';
    info.style.textAlign = 'center';
    info.style.color = '#fff';
    info.style.backgroundColor = 'transparent';
    info.style.zIndex = '1'; // renderer domElement covers it up
    info.style.fontFamily = 'Monospace';
    info.innerHTML = 'How to use renderOrder? <br><br>';
    document.body.appendChild( info );
    
    button = document.createElement( 'button' );
    button.innerHTML = 'Toggle renderOrder'
    button.addEventListener('click', toggleRenderOrder )
    info.appendChild( button )
    
    span = document.createElement( 'span' );
    info.appendChild( span )
	
    function toggleRenderOrder(event) {
        mesh1.renderOrder = mesh1.renderOrder == 0 ? 1 : 0
        mesh2.renderOrder = mesh1.renderOrder == 0 ? 1 : 0 
        span.innerHTML = '<br><br>' 
                    +'mesh1.renderOrder : ' + mesh1.renderOrder + '<br>'
                    +'mesh2.renderOrder : ' + mesh2.renderOrder + '<br>'
    }

    // renderer
    renderer = new THREE.WebGLRenderer();
    renderer.setSize( window.innerWidth, window.innerHeight );
    document.body.appendChild( renderer.domElement );
    renderer.autoClear = false;

    // scene
    scene = new THREE.Scene();
    
    // camera
    camera = new THREE.PerspectiveCamera( 
        40, 
        window.innerWidth / window.innerHeight, 
        1, 
        10000 
    );
    camera.position.set( 50, 50, 150 );

    // controls
    controls = new THREE.OrbitControls( camera, renderer.domElement );
    
    // geometry
    var geometry = new THREE.PlaneGeometry( 50, 50, 1, 1 );
    
    // material
    var material = new THREE.MeshBasicMaterial({
        color: 0xffffff,
        side: THREE.DoubleSide
    });
...