[css-grid-3] Fix masonry-template-tracks grammar to support mixing intrinsic tracks and auto repeats.

Author: tabatkins

css-grid-3/Overview.bs

@@ -571,25 +571,33 @@ Masonry Track Specification</h3>
 
 	<pre class=propdef>
 	Name: masonry-template-tracks
-	Value: <<'grid-template-columns'>>
+	Value: none | <<track-list>> | <<masonry-auto-track-list>> | subgrid <<line-name-list>>?
 	Initial: repeat(auto-areas, auto)
 	Applies to: [=masonry containers=]
 	Inherited: no
-	Percentages: refer to correspodning dimension of the content area
+	Percentages: refer to corresponding dimension of the content area
 	Computed value: by computed value type per item in the [=computed track list=]
 	Animation type: if list lengths match, by [=computed value=] type; otherwise, discrete
 	</pre>
 
-	'masonry-template-tracks' has the same syntax and interpretation as 'grid-template-columns',
-	but a different initial value.
+	The syntax of 'masonry-template-tracks' is a superset of 'grid-template-columns';
+	all shared values have identical interpretations.
+	(The additional values are that <<masonry-auto-track-list>>,
+	unlike <<auto-track-list>> in 'grid-template-columns',
+	allows intrinsic sizes to be combined with auto repetition;
+	see [[#masonry-intrinsic-repeat]] for details.)
 
-	(Instead of defaulting to no tracks, as in Grid Layout,
-	it defaults to matching 'masonry-template-areas', if possible,
-	or otherwise filling the [=masonry container=]
-	with as many ''grid-template-columns/auto'' tracks as possible.)
+	It also has a different initial value:
+	''repeat(auto-areas, auto)'' rather than ''grid-template-columns/none''.
 
 	ISSUE(10869): What should be the initial value?
 
+	<pre class=prod>
+		<dfn>&lt;masonry-auto-track-list></dfn> = [ <<line-names>>? [ <<track-size>> | <<track-repeat>> ] ]*
+		                            <<line-names>>? <<auto-repeat>> <<line-names>>?
+		                            [ [ <<track-size>> | <<track-repeat>> ] <<line-names>>? ]*
+	</pre>
+
 	<pre class=propdef>
 	Name: masonry-template-areas
 	Value: none | <<string>>