[css-flexbox-1][editorial] Link to writing modes' concept of startmost/endmost. w3c#7774 w3c#7776

Author: fantasai

css-flexbox-1/Overview.bs

@@ -2280,7 +2280,7 @@ 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 startmost/endmost <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>
 				is <a lt="generate baselines">generated</a> from
@@ -2310,7 +2310,7 @@ Flex Container Baselines</h3>
 			1. If the flex container has at least one <a>flex item</a>,
 				the flex container's first/last <a>cross-axis baseline set</a>
 				is <a lt="generate baselines">generated</a> from
-				the <a>alignment baseline</a> of the startmost/endmost <a>flex item</a>.
+				the <a>alignment baseline</a> of the [=startmost=]/[=endmost=] <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>