[css-grid-1] Clarify that grid-auto-rows/columns size explicit tracks…

… created by grid-template-areas but not sized by grid-template-rows/columns. #4914

css-grid-1/Overview.bs

@@ -2298,7 +2298,9 @@ The Implicit Grid</h3>
 	<dfn export lt="implicit grid track|implicit grid row|implicit grid column">implicit grid tracks</dfn>
 	by adding <dfn>implicit grid lines</dfn> to the <a>grid</a>.
 	These lines together with the <a>explicit grid</a> form the <dfn export local-lt="implicit">implicit grid</dfn>.
-	The 'grid-auto-rows' and 'grid-auto-columns' properties size these <a>implicit grid tracks</a>.
+	The 'grid-auto-rows' and 'grid-auto-columns' properties size these [=implicit grid tracks=],
+	as well as any [=explicit grid tracks=] created by 'grid-template-areas'
+	but not explicitly sized by 'grid-template-rows' or 'grid-template-columns'
 
 	The 'grid-auto-flow' property controls auto-placement of <a>grid items</a>
 	without an explicit position.
@@ -2335,20 +2337,22 @@ Implicit Track Sizing: the 'grid-auto-rows' and 'grid-auto-columns' properties</
 	Animation type: by computed value type
 	</pre>
 
-	If a grid item is positioned into a row or column that is not explicitly sized
-	by 'grid-template-rows' or 'grid-template-columns',
-	<a>implicit grid tracks</a> are created to hold it.
-	This can happen either by explicitly positioning into a row or column that is out of range,
-	or by the <a>auto-placement algorithm</a> creating additional rows or columns.
-	The 'grid-auto-columns' and 'grid-auto-rows' properties specify the size of such implicitly-created tracks.
-
+	The 'grid-auto-columns' and 'grid-auto-rows' properties specify
+	the size of tracks not assigned a size
+	by 'grid-template-rows' or 'grid-template-columns'.
 	If multiple track sizes are given, the pattern is repeated as necessary
-	to find the size of the implicit tracks.
-	The first <a>implicit grid track</a> after the <a>explicit grid</a>
+	to find the size of the affected tracks.
+	The first track after the last explicitly-sized track
 	receives the first specified size, and so on forwards;
 	and the last <a>implicit grid track</a> before the <a>explicit grid</a>
 	receives the last specified size, and so on backwards.
 
+	Note: If a grid item is positioned into a row or column that is not explicitly declared
+	by 'grid-template-rows'/'grid-template-columns' and/or 'grid-template-areas',
+	[=implicit grid tracks=] are created to hold it.
+	This can happen either by explicitly positioning into a row or column that is out of range,
+	or by the [=auto-placement algorithm=] creating additional rows or columns.
+
 	<div class="example">
 		<pre class="lang-html">
 			&lt;style>