[css-multicol-2] Add column-span: auto

Author: frivoal

css-multicol-2/Overview.bs

@@ -140,7 +140,7 @@ Spanning columns</h2>
 
 	<pre class="parial propdef">
 	Name: column-span
-	Value: none | <<integer>> | all
+	Value: none | <<integer>> | all | auto
 	Initial: none
 	Applies to: in-flow block-level elements
 	Inherited: no
@@ -176,6 +176,22 @@ Spanning columns</h2>
 			</div>
 
 			Issue: <a href="https://figures.spec.whatwg.org/">CSS Figures</a> has evolved into a different approach.
+		<dt><dfn>auto</dfn>
+		<dd>
+			The number of columns spanned by the element
+			depends on its <a>min-content</a> <a>outer size</a>
+			in the inline direction of the <a>multi-column element</a>.
+			If it is smaller than the column width,
+			this is the same as if ''column-span: none'' had been specified.
+			Otherwise, the number of columns spanned is the smallest positive integer <var>n</var>
+			for which <code><var>n</var> × <var>column width</var> + (<var>n</var> - 1) × <var>column gap</var></code>
+			is larger than the <a>min-content</a> <a>outer size</a>.
+			If this would be larger than the number of columns,
+			the number of columns spanned will be the same as if ''column-span: all'' had been specified.
+
+			Issue: If ''column-span: 1'' does not do the same as ''column-span: none'',
+			should this behave as ''column-span: 1'' or as 'column-span: none''
+			when the element is small enough?
 	</dl>
 
 	Issue: Add final content from previous level