The docs for the .width() and .height() methods compare these methods to css('width') and css('height') and say that the only difference is that css() returns a string with the units suffix.

That was true when there was only one CSS box model, but now when the new box-sizing property is set to border-box instead of the default content-box, I think that the css() method will return an entirely different value.

Since browser vendors are starting to implement the border-box style property, I think the documentation needs to be updated.