[css-multicol] definition of column-span should say what happens without an ancestor multicol

[dbaron]

The definition of column-span: all should say what happens if there is no "nearest multicol ancestor in the same block formatting context". This is relatively straightforward; the column-span property doesn't do anything in that case. However, the spec should say so.

/cc @neerjapancholi

[mstensho]

Also probably worth noting that invalid spanners don't force creation of new block formatting contexts and things like that, so that e.g. the following passes:

<!-- Not inside a multicol container. -->
<p>No red should be seen.</p>
<div style="float:left; width:20px; height:20px; background:green;"></div>
<div style="column-span:all; width:20px; height:20px; background:red;"></div>

[tantek]

Agenda+ing just to make sure the WG is ok with this proposal. Figuring we're going to talk a lot of multicol this week.

[astearns]

Removing agenda+ until #1072 is resolved

[dbaron]

This isn't particularly related to #1072, and I think it's trivial enough that it can be resolved at editor discretion if the existing implementations do the obvious thing.

[neerjapancholi]

Tested the case suggested by @mstensho on different browsers and posting results with screenshots:

Test case:
https://jsfiddle.net/Ld86cuwk/

Chrome 56.0.2924.87 (64-bit)	Safari 10.0.3 (11602.4.8.0.1)	Edge 38.14393.0.0
Does not create BFC	Creates BFC	Creates BFC

Screenshot of Chrome:

Screenshot of Safari (same for Edge):

[frivoal]

Firefox agrees with Chrome.
Ignore me, that's just because FF does not implement column-span yet.

[frivoal]

it's trivial [...] if the existing implementations do the obvious thing

Unfortunately, not all do. So we do need to talk…

[mstensho]

So it looks like Chrome is the odd one here, right? In a way I find it strange that a property meant to be used inside multicol containers only has any effect on elements not inside such a container, but the spec does say that column-span applies to "in-flow block-level elements". The spec needs to become clearer. I have no strong opinions when it comes to the exact resolution, other than the fact that it should either be:

A: Chrome has a bug - fix the spec to say that column-span:all outside of multicol still establishes a new block formatting context (on that note: issue #1071 points out that "block formatting context" isn't good wording)

B: Beef up the spec and have the other browsers align with Chrome's behavior

[fantasai]

The case to think about here is, what if the designer had a two-column layout and then switched to a one-column layout. What's least likely to cause breakage? BFCs have to main behaviors that are relevant here: containing floats, and collapsing margins with children. Floats inside column-spanners might be a bit rare, but margins are common. It would imho make sense to preserve the BFC-ness to ensure the children of the spanner don't start collapsing with their parent.

[dbaron]

In Wednesday's WG teleconference the group resolved:

  - RESOLVED: Have column-span elements create a bfc even if not in
              a multi-col container.
  - Florian will clarify the spec in the form of a note.

[yisibl]

PR: Becomes a formatting context: #1179

Chrome fixed it in: https://bugs.chromium.org/p/chromium/issues/detail?id=709362

[frivoal]

@atanassov I've already made the edit almost a week ago (a8634b9) and closed the bug. I guess this Needs Editslabel is a mistake, and that you hadn't seen this was done already. If you actually want some more edits, please let me know what.

@yisibl Thanks for the quick fix in chrome. Would you have some Test cases to submit while you're at it? I'll review them ASAP if you do submit something. Btw, the relevant bug for the #1179 PR is #1071, not this one.