[css-multicol-1] Definition of adjacent spanners

Fixes #6265

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -1195,7 +1195,9 @@ h2 {
 	</div>
 
 	Spanners are block-level boxes 
-	therefore the margins of two adjacent spanners will collapse with each other.
+	therefore the margins of two adjacent spanners will collapse with each other. 
+	The margins of two spanners separated only by an absolutely positioned item will collapse with each other, 
+	as absolutely positioned items do not create column boxes.
 	As column boxes establish a new [=block formatting context=],
 	margins on elements inside a column box will not collapse with the margin of a spanner.
 
@@ -1543,6 +1545,8 @@ This appendix is <em>informative</em>.
 <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>
 
 <ul>
+	<li>Adds the text, "The margins of two spanners separated only by an absolutely positioned item will collapse with each other, 
+	as absolutely positioned items do not create column boxes." <a href="https://github.com/w3c/csswg-drafts/issues/6265#issuecomment-839909999">Resolved 12 May 2021</a></li>
     <li>Adds an accessibility considerations section. <a href="https://github.com/w3c/csswg-drafts/issues/6283">Request from APA after review.</a></li>
 </ul>