[css-grid] Make overlarge grid handling better.

Author: fantasai

css-grid/Overview.bs

@@ -786,14 +786,6 @@ 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>
 
@@ -1484,17 +1476,7 @@ The Implicit Grid</h2>
 	without an explicit position.
 	Once the <a>explicit grid</a> is filled
 	(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.
+	auto-placement 
 
 <h3 id='auto-tracks'>
 Sizing Auto-generated Rows and Columns: the 'grid-auto-rows' and 'grid-auto-columns' properties</h3>
@@ -1748,6 +1730,19 @@ Grid Definition Shorthand: the 'grid' property</h2>
 		</pre>
 	</div>
 
+<h2 id="overlarge-grids">
+Clamping Overlarge Grids</h2>
+
+	Since memory is not infinite,
+	UAs may clamp the the possible size of the <a>grid</a>
+	to within a UA-defined limit,
+	dropping all lines outside that limit.
+	If a <a>grid item</a> spans outside this limit,
+	its span must be clamped to the last line of the limited <a>grid</a>.
+	If a <a>grid item</a> is placed outside this limit,
+	its span must be truncated to 1
+	and the item repositioned into the last <a>grid track</a> on that side of the grid.
+
 <h2 id="placement">
 Placing Grid Items</h2>