[css-grid] Generalize the allowed cap on repetitions to a an allowed limit on grid size.

Author: tabatkins

css-grid/Overview.bs

@@ -726,6 +726,14 @@ The Explicit Grid</h2>
 	Positive indexes count from the before/start side,
 	while negative indexes count from the after/end side.
 
+	Implementations may limit the possible size of the <a>explicit grid</a>.
+	If they do,
+	attempting to specify an <a>explicit grid</a> larger than the implementation-defined maximum
+	must instead define an <a>explicit grid</a> of the maximum size.
+	Implementations may cap the <a>explicit grid</a> to slightly less than the maximum,
+	in order to have only whole repetitions of the ''repeat()'' function.
+	It is recommended that the maximum size of the <a>explicit grid</a> not be smaller than 1 million tracks in each axis.
+
 <h3 id='track-sizing'>
 Track Sizing: the 'grid-template-rows' and 'grid-template-columns' properties</h3>
 
@@ -952,12 +960,6 @@ Repeating Rows and Columns: the ''repeat()'' notation</h4>
 	Note: It is expected that a future level of this specification will define a value to be inserted between the repetitions,
 	similar to the argument of the <code>Array#join</code> method in JavaScript.
 
-	Implementations may cap the maximum number of repetitions they allow.
-	If they do so, they must support at least 10000 repetitions,
-	and if the number of repetitions is greater than the implementation's maximum,
-	the value must be capped to the implementation's maximum
-	(rather than being invalid, overflowing, or some other behavior).
-
 <h4 id='fr-unit'>
 Flexible Lengths: the ''fr'' unit</h4>
 
@@ -1418,6 +1420,16 @@ The Implicit Grid</h2>
 	(or if there is no <a>explicit grid</a>)
 	auto-placement will also cause the generation of <a>implicit grid tracks</a>.
 
+	Implementations may limit the possible size of the <a>implicit grid</a>.
+	If they do,
+	attempting to position (or auto-position) an item past the maximum size
+	must instead position the item with its corresponding edge at the maximum index,
+	possibly overlapping other items.
+	Attempting to size an item to a span past the maximum size
+	must instead size it with a span equal to the maximum size.
+	It is recommended that the maximum size of the <a>implicit grid</a>
+	not be smaller than 1 million tracks in each axis.
+
 <h3 id='auto-tracks'>
 Sizing Auto-generated Rows and Columns: the 'grid-auto-rows' and 'grid-auto-columns' properties</h3>