[css-align-3] Clarify that spanning cells only participate in the first/last row for first/last baseline alignment w3c#7655

Author: fantasai

css-align-3/Overview.bs

@@ -2300,6 +2300,9 @@ Determining the Baselines of a Box</h3>
 			is <a>synthesized</a> from the lowest and highest content edges of the cells in the row.
 			[[!CSS2]]
 
+			Spanning cells participate only in the first/last row that they span
+			for the purpose of ''first baseline''/''last baseline''.
+
 		<dt>flex containers
 		<dd>
 			See <a href="https://www.w3.org/TR/css3-flexbox/#flex-baselines">Flex Baselines</a> in [[!CSS-FLEXBOX-1]].
@@ -2546,6 +2549,9 @@ Changes</h2>
 					</ul>
 				</ins>
 			</blockquote>
+		<li>Clarify that spanning cells only participate in the first/last row they span
+			when participating in first/last baseline alignment.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/7655">Issue 7655</a>)
 		<li>Define the 'grid-gap' properties as [=legacy name aliases=] of the 'gap' properties.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/8014">Issue 8014</a>)
 		<li>Defer definition of ''align-self/normal'' alignment for [=absolutely positioned boxes=] to [[css-position-3]].