[css-multicol-1] spanners inside transforms

Fixes: #6805

Specifies that a spanner can only be created if there is nothing between it and the multicol element that creates a containing block for descendants. Also adds an example using transforms.

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -1120,7 +1120,38 @@ Spanning Columns</h2>
 	</div>
 
 	A spanning element may be lower than the first level of descendants
-	as long as they are part of the same [=formatting context=].
+	as long as they are part of the same [=formatting context=],
+	and there is nothing between the spanning element and [=multicol container=] that establishes a containing block for fixed position descendants.
+
+	<div class="example">
+		In this example, the element with ''column-span: all'' is inside an element with ''transform: rotate(90deg)''. 
+		The transform establishes a containing block for fixed position descendents, 
+		therefore a spanner will not be created.
+
+		<pre highlight="markup">
+		&lt;article&gt;
+			&lt;section&gt;
+				&lt;div class="spanner"&gt;Attempted spanner&lt;/div&gt;
+			&lt;/section&gt;
+		&lt;/article&gt;
+		</pre>
+
+			<pre highlight="css">
+article {
+	columns: 2;
+}
+
+section {
+	transform: rotate(90deg);
+}
+
+.spanner {
+	column-span: all;
+	background: silver;
+}
+</pre>
+	</div>
+
 	If the fragment before the spanner is empty, nothing special happens;
 	the top margin/border/padding is above the spanning element, as an empty [=fragment=].
 
@@ -1564,11 +1595,11 @@ Pagination and Overflow Outside Multicol Containers</h3>
 
 This appendix is <em>informative</em>.
 
-<!-- <h3 id="changes-from-20211012">Changes from the <a href="https://www.w3.org/TR/2021/CR-css-multicol-1-20211012/">Candidate Recommendation (CR) of 12 October 2021</a></h3>
+<h3 id="changes-from-20211012">Changes from the <a href="https://www.w3.org/TR/2021/CR-css-multicol-1-20211012/">Candidate Recommendation (CR) of 12 October 2021</a></h3>
 
 <ul>
-	<li></li>
-</ul> -->
+	<li>Added the text "and there is nothing between the spanning element and [=multicol container=] that establishes a containing block for fixed position descendants." <a href="https://github.com/w3c/csswg-drafts/issues/6805#issuecomment-1063159219">Resolved 9 Mar 2022</a></li>
+</ul>
 
 <h3 id="changes-from-20210212">Changes from the <a href="https://www.w3.org/TR/2021/WD-css-multicol-1-20210212/">Working Draft (WD) of 12 February 2021</a></h3>
 

css-multicol-1/issues-post-cr-2021.txt

@@ -0,0 +1,10 @@
+Draft:    https://www.w3.org/TR/2021/WD-css-multicol-1-20210212/
+Title:    CSS Multi-column Layout Module Level 1
+
+----
+Issue 1.
+Summary:  Prevent column spanners from escaping containing blocks created by transforms.
+From:     Morten Stenshorne
+Comment:  https://github.com/w3c/csswg-drafts/issues/6805
+Closed:   Accepted
+Resolved: https://github.com/w3c/csswg-drafts/issues/6805#issuecomment-1063159219