[csswg-drafts] [cssom] getComputedStyle only supports ::before/::after

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

== [cssom] getComputedStyle only supports ::before/::after ==
https://drafts.csswg.org/cssom/#extensions-to-the-window-interface

Roughly, from what I've tested:

* Chrome, Firefox, and Safari all support gCS `::first-letter` and `::first-line`.
* Firefox throws `NS_ERROR_NOT_AVAILABLE` for `::marker` (and doesn't support `::marker` AFAIK), Chrome doesn't support it so returns the element, and Safari does support `::marker` and does support it for gCS
* Firefox and Safari support gCS `::placeholder`, Chrome does not (despite supporting the feature)

Is there any reason not to allow all pseudo-elements for gCS?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/2149 using your GitHub account