[css-ui] Resize factor?

According to css-ui [1]:
> When an element is resized by the user, the user agent keeps track of a resize factor (which is initially 1.0) for the width and height, which it then applies to the computed width and height as part of determining the used width and height. The element's contents (and surroundings) are reformatted as necessary.

and:
> With regard to interactivity and the Document Object Model (DOM), the resize factor on an element lasts the lifetime of the element, however, if the ‘resize’ property itself is altered (e.g. via pseudo-class change or via DOM manipulation), then the resize factor is reset to 1.0.

So, if I’m reading this right, according to spec the resize factor is only reset if the resize property is dynamically altered. What happens then if width and height are dynamically altered? If the resize factor doesn’t reset, then the author gets completely different dimensions than the ones they used, for no obvious reason. It seems very confusing. 
(Although, none of the browsers I’ve tested seem to actually implement the resize factor anyway. They just modify width/height inline...)

[1]: http://dev.w3.org/csswg/css-ui/#resize

Lea Verou ✿ http://lea.verou.me ✿ @leaverou