[csswg-drafts] [css-lists-3] Define handling of `list-style: inside outside` (#5302)

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

== [css-lists-3] Define handling of `list-style: inside outside` ==
@upsuper wrote in 

>Read through the section of the shorthand, it seems there is current a paragraph describing how `none` in the shorthand can be ambiguous. I guess it would probably be useful to also briefly mention `inside` and `outside` are actually ambiguous as well and they may be recognized as `list-style-type` when there are two such keywords in the shorthand (e.g. `list-style: inside outside;` means `list-style-position: inside; list-style-type: outside;`).

The other option is to make such constructions invalid.
See also https://www.w3.org/TR/css-values-3/#custom-idents

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5302 using your GitHub account