This property can be applied to text elements, but it is most useful with
replaced elements such as images. The width is to be enforced by scaling the
image if necessary. When scaling, the aspect ratio of the image is preserved if
the 'height' property is 'auto'.
Example:
IMG.icon { width: 100px }
If the 'width' and 'height' of a replaced element are both 'auto', these
properties will be set to the intrinsic dimensions of the element.
