[css-grid] Add prose describing when/where content distribution adds space.

Author: fantasai

css-grid/Overview.bs

@@ -2521,7 +2521,7 @@ Aligning the Grid: the 'justify-content' and 'align-content' properties</h3>
 
 	If the <a>grid</a>’s outer edges do not correspond to the <a>grid container</a>’s content edges
 	(for example, if no columns are flex-sized),
-	the <a>grid</a> is aligned within the content box according to the 'justify-content' and 'align-content' properties on the <a>grid container</a>.
+	the <a>grid tracks</a> are aligned within the content box according to the 'justify-content' and 'align-content' properties on the <a>grid container</a>.
 
 	<div class='example'>
 		For example, the following grid is centered vertically,
@@ -2671,6 +2671,13 @@ Overall Sizing Algorithm</h3>
 			</div>
 
 			Issue: Is one cycle enough?
+
+		<li>
+			Finally, the <a>grid container</a> is sized
+			using the resulting size of the <a>grid</a> as its content size,
+			and the tracks are aligned within the <a>grid container</a> 
+			according to the 'align-content' and 'justify-content' properties.
+			<span class="note">Note: This can introduce extra space within or between tracks.</a>
 	</ol>
 
 	Once the size of each <a>grid area</a> is thus established,

css-grid/Overview.html

@@ -746,7 +746,7 @@ <h1 class="p-name no-ref" id="title">CSS Grid Layout Module Level 1</h1>
 
 
       <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft,
-    <time class="dt-updated" datetime="2014-12-19">19 December 2014</time></span></h2>
+    <time class="dt-updated" datetime="2014-12-20">20 December 2014</time></span></h2>
 
 
       <div data-fill-with="spec-metadata">
@@ -4811,7 +4811,7 @@ <h3 class="heading settled" data-level="10.4" id="grid-align"><span class="secno
 
       <p>If the <a data-link-type="dfn" href="#grid">grid</a>’s outer edges do not correspond to the <a data-link-type="dfn" href="#grid-container">grid container</a>’s content edges
 	(for example, if no columns are flex-sized),
-	the <a data-link-type="dfn" href="#grid">grid</a> is aligned within the content box according to the <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-justify-content">justify-content</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-align-content">align-content</a> properties on the <a data-link-type="dfn" href="#grid-container">grid container</a>.</p>
+	the <a data-link-type="dfn" href="#grid-track">grid tracks</a> are aligned within the content box according to the <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-justify-content">justify-content</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-align-content">align-content</a> properties on the <a data-link-type="dfn" href="#grid-container">grid container</a>.</p>
 
 
 
@@ -5031,8 +5031,16 @@ <h3 class="heading settled" data-level="11.2" id="algo-overview"><span class="se
 
           <p class="issue" id="issue-4f54519f"><a class="self-link" href="#issue-4f54519f"></a>Is one cycle enough?</p>
 
-	
+
+		
         </li>
+        <li>
+			Finally, the <a data-link-type="dfn" href="#grid-container">grid container</a> is sized
+			using the resulting size of the <a data-link-type="dfn" href="#grid">grid</a> as its content size,
+			and the tracks are aligned within the <a data-link-type="dfn" href="#grid-container">grid container</a> 
+			according to the <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-align-content">align-content</a> and <a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-align-3/#propdef-justify-content">justify-content</a> properties.
+			<span class="note" role="note">Note: This can introduce extra space within or between tracks.
+	</span></li>
       </ol>