[css-grid] Fix w3c#249 - Be more accurate about which properties are reset, via dholbert.

Author: fantasai

css-grid/Overview.bs

@@ -2156,7 +2156,7 @@ Grid Definition Shorthand: the 'grid' property</h3>
 			'grid-auto-flow' is also set to either ''row'' or ''column'' accordingly,
 			with ''dense'' if it's specified.
 
-			All other properties are reset to their initial values.
+			All other 'grid' <a>sub-properties</a> are reset to their initial values.
 	</dl>
 
 	Note: Note that you can only specify the explicit <em>or</em> the implicit grid properties in a single 'grid' declaration.