[css-grid-1] Clarify that gutters, which are treated as fixed-size tracks, are spanned by any items which span across their corresponding grid line. #2201

Author: fantasai

css-grid-1/Overview.bs

@@ -3253,7 +3253,10 @@ Gutters: the 'row-gap', 'column-gap', and 'gap' properties</h3>
 	the <a>grid track</a> between two <a>grid lines</a>
 	is the space between the <a>gutters</a> that represent them.
 	For the purpose of [[#algo-track-sizing|track sizing]],
-	each <a>gutter</a> is treated as an extra, empty track of the specified size.
+	each <a>gutter</a> is treated as
+	an extra, empty, fixed-size track of the specified size,
+	which is spanned by any <a>grid items</a>
+	that span across its corresponding <a>grid line</a>.
 
 	Note: Additional spacing may be added between tracks
 	due to 'justify-content'/'align-content'.