[css-grid] Distinguish no track preference vs empty preferred tracks. w3c#3648

Author: fantasai

css-grid-1/Overview.bs

@@ -4336,8 +4336,10 @@ Distributing Extra Space Across Spanned Tracks</h4>
 		to accommodate specific intrinsic size contributions (the |size contribution|s)
 		of a set of grid items spanning those tracks (the |item|s),
 		potentially preferring a subset of those tracks
-		(the optional |preferred track|s,
-		defaulting to all |affected track|s):
+		(the optional |preferred track|s);
+		defaulting to all |affected tracks|
+		if there is no |track preference|--
+		as distinct from an empty list of |preferred track|s):
 
 		<ol>
 			<li>
@@ -4402,7 +4404,7 @@ Distributing Extra Space Across Spanned Tracks</h4>
 
 						If extra |space| remains at this point,
 						unfreeze the |preferred track|s (if any)
-						or else the |affected track|s (if not),
+						or else the |affected track|s (if there was no |track preference|),
 						then continue to distribute |space| to the |item-incurred increase| of…
 
 						<ul>

css-grid-2/Overview.bs

@@ -5011,8 +5011,10 @@ Distributing Extra Space Across Spanned Tracks</h4>
 		to accommodate specific intrinsic size contributions (the |size contribution|s)
 		of a set of grid items spanning those tracks (the |item|s),
 		potentially preferring a subset of those tracks
-		(the optional |preferred track|s,
-		defaulting to all |affected track|s):
+		(the optional |preferred track|s);
+		defaulting to all |affected tracks|
+		if there is no |track preference|--
+		as distinct from an empty list of |preferred track|s):
 
 		<ol>
 			<li>
@@ -5077,7 +5079,7 @@ Distributing Extra Space Across Spanned Tracks</h4>
 
 						If extra |space| remains at this point,
 						unfreeze the |preferred track|s (if any)
-						or else the |affected track|s (if not),
+						or else the |affected track|s (if there was no |track preference|),
 						then continue to distribute |space| to the |item-incurred increase| of…
 
 						<ul>