[css-grid] Adding the grid fragmentation section.

--HG--
extra : rebase_source : 5675781616b32ff38a19e398c02874c77a2a9585

Author: Rossen Atanassov

css-grid/Overview.bs

@@ -3023,8 +3023,52 @@ Find the Size of an ''fr''</h4>
 <h2 id='pagination'>
 Fragmenting Grid Layout</h2>
 
-	<p class='issue'>
-		Fill this in.
+	Grid containers break across fragment containers (fragmentainers) [[!CSS3-BREAK]] between
+	grid rows. The break-* properties do not apply to grid areas. When fragmentating grid containers
+	the goal is to minimize the number of grid areas that get fragmented due to their grid row
+	being fragmented.
+
+<h3 id="fragmentation-alg">
+Sample Fragmentation Algorithm</h3>
+
+	<ol>
+		<li>
+			Layout the grid following the <a section href="#layout-algorithm"></a> by using the
+			fragmentainer box width and assume unlimited height. During this step all 'grid-row'
+			''auto'' and ''fr'' values must be resolved.
+
+		<li>
+			Layout the grid container using the values resolved in the previous step.
+
+		<li>
+			If a grid row extends past the current fragment and it is not the first grid row in
+			this fragment; push it to the next fragment. Do this even if the grid row has no items.
+
+		<li>
+			If a grid area dimensions change due to fragmentation (do not include items that
+			span rows in this decision), increase the grid row as necessary for rows that either:
+			<ul>
+				<li>
+					have a content min track sizing function.
+
+				<li>
+					are in a grid that does not have an explicit height and the grid row is flexible.
+			</ul>
+
+		<li>
+			If the grid height is ''auto'', the height of the grid should be the sum of the final
+			row sizes.
+
+		<li>
+			If a grid area overflows the grid container due to margins being collapsed during
+			fragmentation, extend the grid container to contain this grid area (this step is
+			necessary in order to avoid circular layout dependencies due to fragmentation).
+	</ol>
+
+	<p class="note">
+		If the grid’s height is specified, steps three and four may cause the grid rows to
+		overflow the grid.
+	</p>
 
 <h2 class="no-num" id="acks">
 Acknowledgements</h2>