initialize(el, origin, obj) {
      this._el = el;
      this._obj = obj || null;
      return this.origin(origin);
    }
Initialize a new Handler instance.
@param {DOMElement} el - The containing DOM element for the display.
@param {Array<number>} origin - The origin of the display, in pixels.
  The coordinate system will be translated to this point.
@param {object} [obj] - Optional context object that should serve as
  the "this" context for event callbacks.
@return {Handler} - This handler instance.