dojox.fx.style provides a few methods to animate the changes that would occur when adding or removing a class from a domNode.
This is a div position:relative with a position:absolute div inside. testing various t/l/b/r combos. normal css inheritance rules apply, so setting .foo .bar if .foo was defined last in the css text, .bar will take precedent. the below position test shows the results of this:
Some properties cannot be modified (fontFace, and so on), so to ensure the results at the end of the animation are applied correctly and fully, the class name is set on the node via dojo.add/removeClass().