[css-grid] Since fr does nothing in the min slot of minmax(), just make it invalid.

Author: tabatkins

css-grid/Overview.bs

@@ -1120,16 +1120,17 @@ Track Sizing: the 'grid-template-rows' and 'grid-template-columns' properties</h
 	The syntax of a <a>track list</a> is:
 
 	<pre>
-		<dfn>&lt;track-list></dfn>       = [ <<line-names>>? [ <<track-size>> | <<track-repeat>> ] ]+ <<line-names>>?
-		<dfn>&lt;auto-track-list></dfn>  = [ <<line-names>>? [ <<fixed-size>> | <<fixed-repeat>> ] ]+ <<auto-repeat>>
-		                     [ <<line-names>>? [ <<fixed-size>> | <<fixed-repeat>> ] ]+ <<line-names>>?
-		<dfn>&lt;line-name-list></dfn>   = [ <<line-names>> | <<name-repeat>> ]+
-
-		<dfn>&lt;track-size></dfn>       = <<track-breadth>> | minmax( <<track-breadth>> , <<track-breadth>> )
-		<dfn>&lt;fixed-size></dfn>       = <<fixed-breadth>> | minmax( <<fixed-breadth>> , <<track-breadth>> ) | minmax( <<track-breadth>> , <<fixed-breadth>> )
-		<dfn>&lt;track-breadth></dfn>    = <<length>> | <<percentage>> | <<flex>> | min-content | max-content | auto
-		<dfn>&lt;fixed-breadth></dfn>    = <<length>> | <<percentage>>
-		<dfn>&lt;line-names></dfn>       = '[' <<custom-ident>>* ']'
+		<dfn>&lt;track-list></dfn>         = [ <<line-names>>? [ <<track-size>> | <<track-repeat>> ] ]+ <<line-names>>?
+		<dfn>&lt;auto-track-list></dfn>    = [ <<line-names>>? [ <<fixed-size>> | <<fixed-repeat>> ] ]+ <<auto-repeat>>
+		                       [ <<line-names>>? [ <<fixed-size>> | <<fixed-repeat>> ] ]+ <<line-names>>?
+		<dfn>&lt;line-name-list></dfn>     = [ <<line-names>> | <<name-repeat>> ]+
+
+		<dfn>&lt;track-size></dfn>         = <<track-breadth>> | minmax( <<inflexible-breadth>> , <<track-breadth>> )
+		<dfn>&lt;fixed-size></dfn>         = <<fixed-breadth>> | minmax( <<fixed-breadth>> , <<track-breadth>> ) | minmax( <<inflexible-breadth>> , <<fixed-breadth>> )
+		<dfn>&lt;track-breadth></dfn>      = <<length>> | <<percentage>> | <<flex>> | min-content | max-content | auto
+		<dfn>&lt;inflexible-breadth></dfn> = <<length>> | <<percentage>> | min-content | max-content | auto
+		<dfn>&lt;fixed-breadth></dfn>      = <<length>> | <<percentage>>
+		<dfn>&lt;line-names></dfn>         = '[' <<custom-ident>>* ']'
 	</pre>
 
 	Where: