Suppose you had a long animation where you were changing the `width`:

```
var myTargetWidth = 500;
$(el).animate( { "width" : myTargetWidth }, 5000 );

```

The animation is asynchronous so your code continues . . .
a couple seconds later you decide to change the target `width` to `300` . . .
the animation is still running at this point . . .

How would I change targetWidth to a different value on the running animation?