[css3-grid-layout] Sync grid baseline calculations with flexbox.

Author: tabatkins

css3-grid-layout/Overview.html

@@ -310,6 +310,9 @@ <h2 class="no-num no-toc" id=contents> Table of contents</h2>
 
      <li><a href="#z-order"><span class=secno>7.4. </span> Z-axis Ordering:
       the ‘<code class=property>z-index</code>’ property</a>
+
+     <li><a href="#grid-baselines"><span class=secno>7.5. </span> Grid
+      Baselines</a>
     </ul>
 
    <li><a href="#layout-algorithm"><span class=secno>8. </span> Grid Layout
@@ -2480,6 +2483,43 @@ <h3 id=z-order><span class=secno>7.4. </span> Z-axis Ordering: the ‘<code
 	&lt;div id="E">E&lt;/div>
 &lt;/div></pre>
 
+  <h3 id=grid-baselines><span class=secno>7.5. </span> Grid Baselines</h3>
+
+  <p> The baselines of a <a href="#grid-container"><i>grid container</i></a>
+   are determined as follows:
+
+  <ol>
+   <li> If any of the <a href="#grid-item"><i>grid items</i></a> whose areas
+    intersect the <a href="#grid-container"><i>grid container</i></a>’s
+    first row/column <a href="#baseline-participation">participate in
+    baseline alignment</a>, the grid container's baseline is the baseline of
+    those <a href="#grid-item"><i>grid items</i></a>.
+
+   <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.
+
+   <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.
+  </ol>
+
+  <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
+   initial scroll position for the purpose of determining its baseline.
+
+  <p> When <a
+   href="http://www.w3.org/TR/CSS21/tables.html#height-layout">determining
+   the baseline of a table cell</a>, a grid container provides a baseline
+   just as a line box or table-row does. <a href="#CSS21"
+   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a>
+
   <h2 id=layout-algorithm><span class=secno>8. </span> Grid Layout Algorithm</h2>
 
   <h3 id=algo-terms><span class=secno>8.1. </span> Definition of Terms for

css3-grid-layout/Overview.src.html

@@ -1965,6 +1965,42 @@ <h3 id='z-order'>
 	&lt;div id="E">E&lt;/div>
 &lt;/div></pre>
 
+<h3 id='grid-baselines'>
+Grid Baselines</h3>
+
+	<p>
+		The baselines of a <i>grid container</i> are determined as follows:
+
+	<ol>
+		<li>
+			If any of the <i>grid items</i> whose areas intersect the <i>grid container</i>’s first row/column
+			<a href="#baseline-participation">participate in baseline alignment</a>,
+			the grid container's baseline is the baseline of those <i>grid items</i>.
+
+		<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
+			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, 
+			or, failing that, from the grid container's content box.
+	</ol>
+
+	<p>
+		When calculating the baseline according to the above rules,
+		if the box contributing a baseline has an 'overflow' value that allows scrolling,
+		the box must be treated as being in its initial scroll position
+		for the purpose of determining its baseline.
+
+	<p>
+		When <a href="http://www.w3.org/TR/CSS21/tables.html#height-layout">determining the baseline of a table cell</a>,
+		a grid container provides a baseline just as a line box or table-row does. [[!CSS21]]
+
+
+
 <h2 id='layout-algorithm'>
 Grid Layout Algorithm</h2>