constructor(draggable) {
    super(draggable);

    /**
     * Keeps track of currently colliding elements
     * @property {HTMLElement|null} currentlyCollidingElement
     * @type {HTMLElement|null}
     */
    this.currentlyCollidingElement = null;

    /**
     * Keeps track of currently colliding elements
     * @property {HTMLElement|null} lastCollidingElement
     * @type {HTMLElement|null}
     */
    this.lastCollidingElement = null;

    /**
     * Animation frame for finding colliding elements
     * @property {Number|null} currentAnimationFrame
     * @type {Number|null}
     */
    this.currentAnimationFrame = null;

    this[onDragMove] = this[onDragMove].bind(this);
    this[onDragStop] = this[onDragStop].bind(this);
    this[onRequestAnimationFrame] = this[onRequestAnimationFrame].bind(this);
  }
Collidable constructor.
@constructs Collidable
@param {Draggable} draggable - Draggable instance