[css-align-3] Align table baseline alignment with compat requirements

Author: fantasai

css-align-3/Overview.bs

@@ -2145,7 +2145,8 @@ Determining the Baselines of a Box</h3>
 		<dt>tables
 		<dd>
 			The first/last [=baseline set=] of a table box
-			is the first/last [=baseline set=] of its first/last row.
+			is the first/last [=baseline set=] of its first/last row
+			(after any reordering of [=table row groups=]).
 
 			When finding the first/last baseline set of an inline-block,
 			any baselines contributed by table boxes must be skipped.
@@ -2166,23 +2167,30 @@ Determining the Baselines of a Box</h3>
 				last [=baseline alignment=] along the table’s [=inline axis=],
 				[=generate=] from <em>that</em> [=alignment baseline=].
 
+			<!-- Other layout models have this step, but for compat reasons tables can't.
 			3.  Otherwise, if any cells in the row have an [=inline-axis=] [=baseline set=] at all,
 				take the [=baseline set=] from the cell
 				with the <em>highest</em> ([=block-start=]&ndash;most) baseline
 				corresponding to the table's [=alignment baseline=].
+			-->
 
-			4.  Otherwise, [=synthesize=] from the lowest and highest [=content edges=]
+			4.  Otherwise, if the row is not empty,
+				[=synthesize=] from the lowest and highest [=content edges=]
 				of all the cells in the row.
-				(See [[!CSS2]].)
+				See [[css2#height-layout]].
+
+			5.  Otherwise,
+				use the [=block-start=] [=content edge=] of the [=table row box=] itself
+				as the [=alignment baseline=].
 
 			For this purpose,
 			any [=table cell=] that spans multiple rows
 			is ignored if it’s span does not start in this row;
 			except that for step 2,
 			it's ignored if its span does not <em>end</em> in this row.
 
-			Last baselines are analogous
-			(with “first”/“last” and “start”/“end” inverted).
+			<em>Last baselines are analogous
+			(with “first”/“last” and “start”/“end” inverted).</em>
 
 			Spanning cells participate only in the first/last row that they span
 			for the purpose of ''first baseline''/''last baseline''.