[css-flexbox] Talk about startmost/endmost, and explicitly ref flex-direction, so you get the visually-correct baseline.

Author: tabatkins

css-flexbox/Overview.bs

@@ -2178,7 +2178,9 @@ Flex Container Baselines</h3>
 	(e.g. when the <a>flex container</a> is itself a <a>flex item</a> in an outer <a>flex container</a>),
 	it needs to submit the position of the baselines that will best represent its contents.
 	To this end,
-	the baselines of a flex container are determined as follows (after reordering with 'order'):
+	the baselines of a flex container are determined as follows
+	(after reordering with 'order',
+	and taking 'flex-direction' into account):
 
 	<dl>
 		<dt>first/last <dfn export id="main-axis-baseline"
@@ -2189,22 +2191,22 @@ Flex Container Baselines</h3>
 			matches its <a>main axis</a>,
 			its baselines are determined as follows:
 
-			1. If any of the <a>flex items</a> on the flex container's first/last <a>flex line</a>
+			1. If any of the <a>flex items</a> on the flex container's startmost/endmost <a>flex line</a>
 				<a href="#baseline-participation">participate in baseline alignment</a>,
-				the flex container's first/last <a>main-axis baseline set</a>
+				the flex container's startmost/endmost <a>main-axis baseline set</a>
 				is <a lt="generate baselines">generated</a> from
 				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>,
-				the flex container's first/last <a>main-axis baseline set</a>
+				the flex container's startmost/endmost <a>main-axis baseline set</a>
 				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>main axis</a>,
 				then one is first <a lt="synthesized baseline">synthesized</a>
 				from its border edges.)
 
-			3. Otherwise, the flex container has no first/last main-axis <a>baseline set</a>,
+			3. Otherwise, the flex container has no startmost/endmost 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>.