/**
 * Abstract Tween base object.
 * Uses `ease npm` for all ease functions.
 * For ease types, refer to [ease APIs]{@link https://www.npmjs.com/package/eases}.
 * @class Tween
 * @memberof jibo.face
 */

    /**
     * `true` if the tween is to be paused.
     * @name jibo.face.Tween#paused
     * @type {Boolean}
     */

    /**
     * The local lerp value for just this tween.
     * @name jibo.face.Tween#_time
     * @type {Number}
     * @protected
     */

    /**
     * Duration in milliseconds.
     * @name jibo.face.Tween#_duration
     * @type {Number}
     * @protected
     */

    /**
     * Finished callback
     * @name jibo.face.Tween#_complete
     * @type {Function}
     * @private
     */

    /**
     * Flag used to block tween from being manually stopped.
     * @name jibo.face.Tween#_inProcess
     * @type {Boolean}
     * @private
     */

    /**
     * the number of milliseconds to delay this tween from playing from the time it was added to the TweenMgr
     * @name jibo.face.Tween#_delay
     * @type {Number}
     * @private
     */

    /**
     * Elapsed time in milliseconds
     * @name jibo.face.Tween#_elapsed
     * @type {Number}
     * @private
     */

    /**
     * Starting value
     * @name jibo.face.Tween#_start
     * @type {Object}
     * @private
     */

    /**
     * Ending value
     * @name jibo.face.Tween#_end
     * @type {Object}
     * @private
     */

    /**
     * Ease callback.
     * @name jibo.face.Tween#_ease
     * @type {Function}
     * @private
     */

    /**
     * Target for tweening.
     * @name jibo.face.Tween#_target
     * @type {Object}
     * @private
     */

    /**
     * Initial the tween.
     * @method jibo.face.Tween#init
     * @param {*} [target] The thing to tween.
     * @param {Object} options Options for tweening.
     * @param {Object} [options.to] The values to tween the object to.
     * @param {Object} [options.from] The initial values to set the object to.
     * @param {String} [options.ease='linear'] The ease function to use.
     * @param {int} [options.delay=0] The delay to start.
     * @param {int} [options.duration=500] Length of tween, in millseconds.
     * @param {Function} [complete] Callback function, if any.
     */

    /**
     * Update the tween value.
     * @method jibo.face.Tween#reset
     * @param {Number} v0 start number
     * @param {Number} v1 end number
     * @param {Number} t Time
     * @private
     */

    /**
     * The delay of start of tween in milliseconds.
     * @name jibo.face.Tween#delay
     * @type {Number}
     */

    /**
     * The duration of this tween.
     * @name jibo.face.Tween#duration
     * @type {Number}
     * @readOnly
     */

    /**
     * The current time from 0 to 1.
     * @name jibo.face.Tween#time
     * @type {Number}
     * @readOnly
     */

    /**
     * The target to tween.
     * @name jibo.face.Tween#target
     * @type {any}
     * @readOnly
     */

    /**
     * Flag indicating if tween is in a process that should not be manually stopped.
     * @name jibo.face.Tween#inProcess
     * @type {Boolean}
     * @readOnly
     */

    /**
     * Call the finished callback.
     * @method jibo.face.Tween#completed
     */

        /**
         * Event when tween is completed.
         * @event jibo.face.Tween#complete
         * @param {*} target The target of tween.
         */

    /**
     * Update the tween value.
     * @method jibo.face.Tween#update
     * @param {Number} elapsed Milliseconds since the last update.
     */

        /**
         * Event when tween value has changed.
         * @event jibo.face.Tween#change
         * @param {*} value The value or values set.
         * @param {*} target The target of tween.
         */

    /**
     * Assign a collection of properties.
     * @method jibo.face.Tween#assign
     * @param {Object} values Map of properties to set
     * @private
     */

    /**
     * Assign a specific property and value to the target.
     * @method jibo.face.Tween#assignValue
     * @param {String} prop Property name.
     * @param {Number|String} value Value to set.
     * @private
     */

    /**
     * Update the tween value.
     * @method jibo.face.Tween#lerp
     * @param {Number} v0 start number
     * @param {Number} v1 end number
     * @param {Number} t Time
     * @private
     */

    /**
     * Auto-generate the start key values.
     * @method jibo.face.Tween#startDefaults
     * @param {Object} to end keys
     * @private
     * @return {Object} Default start keys
     */

    /**
     * Auto-generate the end key values.
     * @method jibo.face.Tween#endDefaults
     * @param {Object} from start keys
     * @private
     * @return {Object} Default end keys
     */

    /**
     * Check that both objects have the same keys.
     * @method jibo.face.Tween#validate
     * @private
     * @param {Object|Number} obj1 Object 1 to compare
     * @param {Object|Number} obj2 Object 2 to compare
     * @return {Boolean} `true` if both have the same keys.
     */