Right, the issue here is that we don't have enough semantic control over why an element is a certain size in CSS. One of the underlying reasons why `em`/`rem`

Right, the issue here is that we don't have enough semantic control over why an element is a certain size in CSS. One of the underlying reasons why `em`/`rem` units tend to work better in CSS for container widths is because very often semantically you want to design a column in relation to how many characters of text it should display in a row before wrapping. But not always; case in point touch interfaces where the reason everything is getting bigger is not because anything fundamental has changed about the user's text preferences, but because bigger elements are necessary for a bigger pointer. So it does kind of make sense to me that we could have a semantic unit that is unrelated to text size and specifically related to a user/device defined touch size. And then you could have a mix of min/max widths and heights based on different semantic units to have something that responds equally well to both narrow windows on the desktop and mobile devices. I am all for having more sizing units that are based on user-defined attributes that are applicable to a specific category of measurement (font-size, touch-precision, screen-brightness, whatever), not on trying to guess what specific device a user has.