public Then(TweenNode expr, ASTNode body)
 {
     Expr = expr;
     Body = body;
 }
 public Animate(TweenNode expr, Arguments args)
 {
     Expr = expr;
     Args = args;
 }
 public Ease(string id, TweenNode expr, Arguments args)
 {
     Id   = id;
     Expr = expr;
     Args = args;
 }
 public Delay(TweenNode expr, Arguments args)
 {
     Expr = expr;
     Args = args;
 }
 public From(TweenNode expr, Arguments args, bool relative)
 {
     Expr     = expr;
     Args     = args;
     Relative = relative;
 }