docs: function() {
    // Define our control key codes and states.
    this.codes = {
      // Arrows
      37: 'left', 39: 'right', 38: 'front', 40: 'back',
      // WASD
      65: 'left', 68: 'right', 87: 'front', 83: 'back',
    };
    this.states = {left: false, right: false, front: false, back: false};
  
    // Setup the DOM listeners.
    document.addEventListener('keydown', this.key.bind(this, true), false);
    document.addEventListener('keyup', this.key.bind(this, false), false);
    document.addEventListener('touchstart', this.touch.bind(this), false);
    document.addEventListener('touchmove', this.touch.bind(this), false);
    document.addEventListener('touchend', this.touchEnd.bind(this), false);
  }