[css-grid-1] Clarify antecedents for flexible tracks. #4544

Author: tabatkins

css-grid-1/Overview.bs

@@ -4390,7 +4390,7 @@ Expand Flexible Tracks</h3>
 	using the largest value it can assign to an ''fr''
 	without exceeding the <a>available space</a>.
 
-	First, find the used <a>flex fraction</a>:
+	First, find the grid's used <a>flex fraction</a>:
 
 	<dl>
 		<dt>If the <a>free space</a> is zero
@@ -4411,12 +4411,15 @@ Expand Flexible Tracks</h3>
 
 			<ul>
 				<li>
-					If the flexible track's <a>flex factor</a> is greater than one,
+					For each flexible track,
+					if the flexible track's <a>flex factor</a> is greater than one,
 					the result of dividing the track's <a>base size</a> by its <a>flex factor</a>;
 					otherwise,
 					the track's <a>base size</a>.
 
-				<li>The result of
+				<li>
+					For each [=grid item=] that crosses a flexible track,
+					the result of
 					<a href="#algo-find-fr-size">finding the size of an fr</a>
 					for each <a>grid item</a> that crosses a flexible track,
 					using all the grid tracks that the item crosses