* Tween type - bit field of `FlxTween`'s static type constants.
@:optionaloptionalstartDelay:Null<Float>
* Seconds to wait until starting this tween, `0` by default.
* Optional update callback function.
* Optional start callback function.
* Optional complete callback function.
@:optionaloptionalloopDelay:Null<Float>
* Seconds to wait between loops of this tween, `0` by default.
* Optional easer function (see `FlxEase`).