[css-align] Column flexboxes can't align-content, because the axises aren't aligned right. #3005

Author: tabatkins

css-align-3/Overview.bs

@@ -54,6 +54,7 @@ spec:css-overflow-3; type:dfn; text:scroll container
 spec:css-position-3; type:property; text:left
 spec:css-writing-modes-3; type:dfn; text:dominant baseline
 spec:selectors-3; type:dfn; text:first formatted line
+spec:css2; type:dfn; text:line box
 </pre>
 
 <style>
@@ -1138,6 +1139,12 @@ Baseline Content-Alignment</h3>
 	to align the <a>alignment baseline</a> of its contents
 	with that of other baseline-aligned boxes in its <a>baseline-sharing group</a>.
 
+	[=Baseline content-alignment=] can only apply if the 'align-content' axis
+	is parallel with the box's [=block axis=]
+	(i.e. it does not apply to “column” [=flex containers=]);
+	otherwise the [=fallback alignment=] is used.
+
+
 	The set of boxes that participate in <a>baseline content-alignment</a>
 	depends on the layout model: