[css-grid] Use synthesized border-box baseline for grid items without a natural baseline in the right axis. <#373> per WG resolution <https://lists.w3.org/Archives/Public/www-style/2016Sep/0000.html>

Author: fantasai

css-flexbox/Overview.bs

@@ -2174,24 +2174,17 @@ Flex Container Baselines</h3>
 				the shared <a>alignment baseline</a> of those <a>flex items</a>.
 
 			2. Otherwise, if the flex container has at least one <a>flex item</a>,
-				and its first/last <a>flex item</a> has a baseline
-				parallel to the flex container's <a>main axis</a>,
 				the flex container's first/last <a>main-axis baseline set</a>
 				is <a lt="generate baselines">generated</a> from
-				its <a>alignment baseline</a>.
-
-			3. Otherwise, the flex container has no natural first/last main-axis <a>baseline set</a>,
-				and a synthesized first/last <a>baseline set</a>, if needed,
-				is <a lt="synthesize baselines">synthesized</a>
-				from the first/last item's border box,
-				or, failing that, from the flex container's content box.
+				the <a>alignment baseline</a> of the first/last <a>flex item</a>.
+				(If that item has no <a>alignment baseline</a>
+				parallel to the flex container's <a>main axis</a>,
+				then one is first <a lt="synthesized baseline">synthesized</a>
+				from its border edges.)
 
-				<!--
-					Logic behind this choice (because it's different than other baseline calculations):
-					If a flexbox has content, the baseline will definitely be inside the flexbox's content box.
-					Thus, using the *flexbox's* content box keeps this fairly consistent -
-					you don't suddenly jump outside the content box when you delete the last bit of content.
-				-->
+			3. Otherwise, the flex container has no first/last main-axis <a>baseline set</a>,
+				and one is <a lt="synthesize baselines">synthesized</a> if needed
+				according to the rules of its <a>alignment context</a>.
 
 		<dt>first/last <dfn export id="cross-axis-baseline"
 			lt="cross-axis baseline set|first cross-axis baseline set|last cross-axis baseline set">
@@ -2202,16 +2195,18 @@ Flex Container Baselines</h3>
 			its baselines are determined as follows:
 
 			1. If the flex container has at least one <a>flex item</a>,
-				and its first/last <a>flex item</a> has a first/last <a>baseline set</a>
-				parallel to the flex container's <a>cross axis</a>,
 				the flex container's first/last <a>cross-axis baseline set</a>
-				is that baseline set.
+				is <a lt="generate baselines">generated</a> from
+				the <a>alignment baseline</a> of the first/last <a>flex item</a>.
+				(If that item has no <a>alignment baseline</a>
+				parallel to the flex container's <a>cross axis</a>,
+				then one is first <a lt="synthesized baseline">synthesized</a>
+				from its border edges.)
+
+			2. Otherwise, the flex container has no first/last main-axis <a>baseline set</a>,
+				and one is <a lt="synthesize baselines">synthesized</a> if needed
+				according to the rules of its <a>alignment context</a>.
 
-			2. Otherwise, the flex container has no natural cross-axis <a>baseline set</a>,
-				and a synthesized first/last <a>baseline set</a>, if needed,
-				is <a lt="synthesize baselines">synthesized</a>
-				from the first/last item's border box,
-				or, failing that, from the flex container's content box.
 	</dl>
 
 	When calculating the baseline according to the above rules,

css-grid/Overview.bs

@@ -3514,20 +3514,18 @@ Grid Container Baselines</h3>
 			the shared <a>alignment baseline</a> of those <a>grid items</a>.
 
 		<li>
-			Otherwise, if the grid container has at least one <a>grid item</a> whose area intersects the first (last) row/column,
-			and the first (last) such <a>grid item</a> (in <a>grid order</a>)
-			has a baseline set parallel to the relevant axis,
-			the grid container's first (last) baseline set in that axis
+			Otherwise, if the grid container has at least one <a>grid item</a> whose area intersects the first (last) row,
+			the grid container's first (last) baseline set
 			is <a lt="generate baselines">generated</a> from
-			that <a>grid item</a>’s <a>alignment baseline</a>.
+			the <a>alignment baseline</a> of the first (last) such <a>grid item</a> (in <a>grid order</a>).
+			If the item has no <a>alignment baseline</a> in that axis,
+			then one is first <a lt="synthesize baselines">synthesized</a>
+			from its border edges.
 
 		<li>
-			Otherwise, the grid container has no natural first (last) <a>baseline set</a> in that axis,
-			and a synthesized first/last <a>baseline set</a>, if needed,
-			is <a lt="synthesize baselines">synthesized</a>
-			from the first (last) item's (in <a>grid order</a>) content box,
-			or, if there's no <a>grid item</a>,
-			from the grid container's content box.
+			Otherwise, the grid container has no first (last) <a>baseline set</a>,
+			and one is <a lt="synthesize baselines">synthesized</a> if needed
+			according to the rules of its <a>alignment context</a>.
 	</ol>
 
 	<dfn export lt="grid order|grid-modified document order">'grid-modified document order (grid order)</dfn>