text: var BriefPlayer = require('./BriefPlayer');
  
  /**
   *
   * @classdesc
   * Manages tweening of one property or several properties of an object
   *
   * @param {object} element Object to tween
   * @param {string} property Property to tween
   * @param {number} a starting value of property
   * @param {number} b ending value of property
   *
   */
  
  function Timeline() {
  	if ((this instanceof Timeline) === false) {
  		return new Timeline();
  	}
  
  	BriefPlayer.call(this);
  }
  Timeline.prototype = Object.create(BriefPlayer.prototype);
  Timeline.prototype.constructor = Timeline;
  module.exports = Timeline;
  
  Timeline.prototype.add = function (playable, startTime) {
  	if (startTime === null || startTime === undefined) {
  		startTime = 0;
  	}
  
  	playable._setStartTime(startTime);
  	this._add(playable);
  
  	var endTime = playable._getEndTime();
  	if (endTime > this._duration) {
  		this._setDuration(endTime);
  	}
  
  	return this;
  };