[css-grid-1] Update Changes section

Author: fantasai

css-grid-1/Overview.bs

@@ -5018,6 +5018,32 @@ Minor Changes</h4>
 Clarifications</h4>
 
 	<ul>
+		<li id="change-2017-implicitly-sized-explicit-tracks">
+			Clarified that 'grid-auto-rows' and 'grid-auto-columns' apply to
+			[=explicit tracks=] created by 'grid-template-areas'
+			that are not assigned a size by 'grid-template-rows' or 'grid-template-columns'.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/4914">Issue 4914</a>)
+			<blockquote>
+				<p>&hellip; These lines together with the <a>explicit grid</a> form the [=implicit grid=].
+				The 'grid-auto-rows' and 'grid-auto-columns' properties size these [=implicit grid tracks=]<ins>,
+				as well as any [=explicit tracks=] created by 'grid-template-areas'
+				but not explicitly sized by 'grid-template-rows' or 'grid-template-columns'</ins></p>
+			</blockquote>
+			<blockquote>
+				<p>The 'grid-auto-columns' and 'grid-auto-rows' properties specify
+				the size of <del>such implicitly-created tracks</del>
+				<ins>tracks not assigned a size
+				by 'grid-template-rows' or 'grid-template-columns'.</ins>
+			</blockquote>
+			<blockquote>
+				If multiple track sizes are given, the pattern is repeated as necessary
+				to find the size of the <del>implicit</del><ins>affected</ins> tracks.
+				The first <del>implicit grid</del> track after the <del>explicit grid</del>
+				<ins>last explicitly-sized</ins> 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.
+			</blockquote>
 		<li id="change-2017-gutter-tracks">
 			Added reminder to <a>track sizing algorithm</a>
 			that gutters are treated as fixed-size tracks;