[css-grid] Move Clamping section to be a subsection because it's ridiculous as a top-level section.

Author: fantasai

css-grid/Overview.bs

@@ -759,6 +759,54 @@ Sizing Grid Containers</h3>
 
 	See [[!CSS3-SIZING]] for a definition of the terms in this section.
 
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+
+<h3 id="overlarge-grids">
+Clamping Overlarge Grids</h3>
+
+	Since memory is not infinite,
+	UAs may clamp the possible size of the <a>grid</a>
+	to within a UA-defined limit,
+	dropping all lines outside that limit.
+	If a grid item is placed outside this limit,
+	its grid area must be <a>clamped</a> to within this limited grid.
+
+	To <dfn local-lt=clamp>clamp a grid area</dfn>:
+	* If the <a>grid area</a> would span outside the limited grid,
+		its span is clamped to the last line of the limited <a>grid</a>.
+	* If the <a>grid area</a> would be placed completely outside the limited grid
+		its span must be truncated to 1
+		and the area repositioned into the last <a>grid track</a> on that side of the grid.
+
+	<div class='example'>
+		For example, if a UA only supported grids with at most 1000 tracks in each dimension,
+		the following placement properties:
+
+		<pre class="lang-css">
+		.grid-item {
+			grid-row: 500 / 1500;
+			grid-column: 2000 / 3000;
+		}
+		</pre>
+
+		Would end up being equivalent to:
+
+		<pre class="lang-css">
+		.grid-item {
+			grid-row: 500 / 1001;
+			grid-column: 1000 / 1001;
+		}
+		</pre>
+	</div>
+
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@@ -2310,54 +2358,6 @@ Grid Definition Shorthand: the 'grid' property</h2>
 	Issue: The auto-placed grid shorthand syntax isn't particularly useful.
 	An auto-placed grid needs an auto axis, but also an explicit axis.
 
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--->
-
-<h2 id="overlarge-grids">
-Clamping Overlarge Grids</h2>
-
-	Since memory is not infinite,
-	UAs may clamp the possible size of the <a>grid</a>
-	to within a UA-defined limit,
-	dropping all lines outside that limit.
-	If a grid item is placed outside this limit,
-	its grid area must be <a>clamped</a> to within this limited grid.
-
-	To <dfn local-lt=clamp>clamp a grid area</dfn>:
-	* If the <a>grid area</a> would span outside the limited grid,
-		its span is clamped to the last line of the limited <a>grid</a>.
-	* If the <a>grid area</a> would be placed completely outside the limited grid
-		its span must be truncated to 1
-		and the area repositioned into the last <a>grid track</a> on that side of the grid.
-
-	<div class='example'>
-		For example, if a UA only supported grids with at most 1000 tracks in each dimension,
-		the following placement properties:
-
-		<pre class="lang-css">
-		.grid-item {
-			grid-row: 500 / 1500;
-			grid-column: 2000 / 3000;
-		}
-		</pre>
-
-		Would end up being equivalent to:
-
-		<pre class="lang-css">
-		.grid-item {
-			grid-row: 500 / 1001;
-			grid-column: 1000 / 1001;
-		}
-		</pre>
-	</div>
-
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