[css-align-3] Clarify that boxes participating in baseline content-al…

…ignment and baseline self-alignment align together. #3200

css-align-3/Overview.bs

@@ -2176,6 +2176,14 @@ Baseline Alignment Grouping</h3>
 			(i.e., the baselines that want to align are on the same side of the alignment context).
 	</ul>
 
+	Note: Boxes participating in <a>baseline content-alignment</a> and
+	boxes participating in <a>baseline self-alignment</a>
+	can be part of the same <a>baseline-sharing group</a>,
+	and can thus align to each other.
+	The difference between the two methods
+	is in where extra space is inserted to perform the alignment
+	(inside or outside the box’s own border).
+
 	Boxes share an <dfn lt="shared alignment context|alignment context" export>alignment context</dfn>,
 	along a particular axis,
 	and established by a particular box,