[css3-grid-layout] Define order-modified grid order for baseline calculations.

Author: tabatkins

css3-grid-layout/Overview.html

@@ -2498,17 +2498,28 @@ <h3 id=grid-baselines><span class=secno>7.5. </span> Grid Baselines</h3>
    <li> Otherwise, if the grid container has at least one <a
     href="#grid-item"><i>grid item</i></a> whose area intersects the first
     row/column, and the first such <a href="#grid-item"><i>grid item</i></a>
-    (in ‘<code class=property>order</code>’-modified document order) has
-    a baseline parallel to the relevant axis, the grid container's baseline
-    is that baseline.
+    (in <a href="#order-modified-grid-order"><i>‘<code
+    class=property>order</code>’-modified grid order</i></a>) has a
+    baseline parallel to the relevant axis, the grid container's baseline is
+    that baseline.
 
    <li> Otherwise, the grid container's baseline is <a
     href="http://www.w3.org/TR/css3-writing-modes/#inline-alignment">synthesized</a>
-    from the first item's (in ‘<code
-    class=property>order</code>’-modified document order) content box, or,
-    failing that, from the grid container's content box.
+    from the first item's (in <a
+    href="#order-modified-grid-order"><i>‘<code
+    class=property>order</code>’-modified grid order</i></a>) content box,
+    or, failing that, from the grid container's content box.
   </ol>
 
+  <p> <dfn id=order-modified-grid-order>‘<code
+   class=property>order</code>’-modified grid order</dfn> is the order in
+   which <a href="#grid-item"><i>grid items</i></a> are encountered when
+   traversing the grid's <i>grid cells</i>, in row-major order if calculating
+   the inline-axis baseline, or in column-major order if calculating the
+   block-axis baseline. If two items are encountered at the same time, they
+   are taken in ‘<code class=property>order</code>’-modified document
+   order.
+
   <p> When calculating the baseline according to the above rules, if the box
    contributing a baseline has an ‘<code class=property>overflow</code>’
    value that allows scrolling, the box must be treated as being in its
@@ -3741,6 +3752,10 @@ <h2 class=no-num id=index> Index</h2>
    <li>‘<a href="#none"><code class=css>none</code></a>’, <a href="#none"
     title="section 6.3."><strong>6.3.</strong></a>
 
+   <li>‘<code class=property>order</code>’-modified grid order, <a
+    href="#order-modified-grid-order"
+    title="section 7.5."><strong>7.5.</strong></a>
+
    <li>RemainingSpace, <a href="#RemainingSpace-definition"
     title="section 8.1."><strong>8.1.</strong></a>
 

css3-grid-layout/Overview.src.html

@@ -1979,16 +1979,24 @@ <h3 id='grid-baselines'>
 
 		<li>
 			Otherwise, if the grid container has at least one <i>grid item</i> whose area intersects the first row/column,
-			and the first such <i>grid item</i> (in 'order'-modified document order) has a baseline
+			and the first such <i>grid item</i> (in <i>'order'-modified grid order</i>) has a baseline
 			parallel to the relevant axis,
 			the grid container's baseline is that baseline.
 
 		<li>
 			Otherwise, the grid container's baseline is <a href="http://www.w3.org/TR/css3-writing-modes/#inline-alignment">synthesized</a> 
-			from the first item's (in 'order'-modified document order) content box, 
+			from the first item's (in <i>'order'-modified grid order</i>) content box, 
 			or, failing that, from the grid container's content box.
 	</ol>
 
+	<p>
+		<dfn>'order'-modified grid order</dfn> is the order in which
+		<i>grid items</i> are encountered when traversing the grid's <i>grid cells</i>,
+		in row-major order if calculating the inline-axis baseline,
+		or in column-major order if calculating the block-axis baseline.
+		If two items are encountered at the same time,
+		they are taken in 'order'-modified document order.
+
 	<p>
 		When calculating the baseline according to the above rules,
 		if the box contributing a baseline has an 'overflow' value that allows scrolling,