[csswg-drafts] [css-values-4][cssom] <resolution> serializes to 'dppx', not 'x'

csnardi has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-values-4][cssom] <resolution> serializes to 'dppx', not 'x' ==
After #461, [Values 4 states that](https://drafts.csswg.org/css-values-4/#resolution):

> All \<resolution\> units are compatible, and 'x' is their canonical unit.

However, [the CSSOM spec](https://drafts.csswg.org/cssom/#serializing-css-values) for serializing \<resolution\> says:

> The resolution in dots per CSS pixel serialized as per \<number\> followed by the literal string "dppx".

The Typed OM spec also makes no mention of 'x', [only 'dppx'](https://drafts.css-houdini.org/css-typed-om-1/#dom-css-dppx).

Should the canonical unit for \<resolution\> be changed back to 'dppx'? Changing all of these serializations to 'x' from 'dppx' might not be web-compatible, and would result in differences in serialization among browsers.


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/2241 using your GitHub account