[css-multicol-2] Add ::column pseudo, per WG resolution. #10715

[tabatkins]

@frivoal @rachelandrew Hi y'all, just drafting the ::column pseudo per #10715. Feel free to review/merge. I can also move the new section elsewhere if desired (or, potentially, to the Pseudo spec instead, but I feel like this is the better spot for it).

[fantasai]

I'm not sure this is true. I think we might reasonably say that they do wrap the contents of the column; and in the far future when we allow fragment-based styling, we might want to.

[tabatkins]

We very specifically resolved that ::column was a leaf node, with no contents. See #10715 (comment) You even made some comments in support of that. ^_^

[tabatkins]

Do we want to add 'scroll-behavior' to the list of supported ::column properties? It's the only thing checked on the element by the perform a scroll algorithm, just to see if the scroll should be smooth or not. (While you can't (yet) scroll to a ::column via JS, the same algo is invoked when you click the ::scroll-marker associated with the ::column.)

[rachelandrew]

I think here is as good a place as any for it for now, we could always move it later. Unless @frivoal has concerns I'm happy to merge it here.

[AmeliaBR]

Is there an open issue for discussing which other properties might apply to a ::column pseudo-element? As suggested in:

Note: This list of properties and pseudo-elements that work on ::column will likely be expanded in the future, as we develop more features that could usefully care about the position of a column without caring about the contents.

For example, I think it would be safe to add a background color & maybe full backgrounds, if someone wanted the column area to be coloured but not the gaps. Although then there might be a desire to add padding around the text but inside the coloured area, and... yeah, that's why there should probably be a standing issue (linked from that note) where you can start scoping out what is or isn't possible for this psuedo-element.

[rachelandrew]

@AmeliaBR I don't think we specifically have an issue for multicol, there's mention of fragment styling in overflow-4 which would be one way to achieve this. It's definitely something people ask for.