[csswg-drafts] [css-multicol] Margin collapsing does not make sense with column-spans.

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

== [css-multicol] Margin collapsing does not make sense with column-spans. ==
I'm filing this based on a discussion I just had with @dbaron. 

It seems like the multicol spec does not forbid margin collapsing with column-span elements. So the margin of a column-span can collapse w.r.t. just one column and that doesn't make sense. Also, the spec mentions that a multicol element itself creates a BFC but does not specifically say that the columns inside it also create a BFC. This might clarify the margin collapsing behavior for column-spans.

An example of an existing test where this can be seen is -
https://github.com/w3c/web-platform-tests/blob/master/css/css-multicol/multicol-span-all-margin-bottom-001.xht

Screenshots of Chrome - (Orange and black bands are the column-spans)
![screen shot 2018-01-18 at 4 30 16 pm](https://user-images.githubusercontent.com/5490554/35129145-00e4b164-fc6f-11e7-9499-3dc5a3ad1966.jpg)


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/2203 using your GitHub account