[css-align] Clarify what justify-self:auto does on a root element.

Author: tabatkins

css-align/Overview.bs

@@ -624,7 +624,8 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 	The <dfn value for="justify-self">auto</dfn> keyword computes to
 	itself on absolutely-positioned elements,
 	and to the computed value of 'justify-items' on the parent
-	(minus any ''legacy'' keywords) on all other boxes.
+	(minus any ''legacy'' keywords) on all other boxes,
+	or ''start'' if the box has no parent.
 
 	<hr>
 
@@ -724,7 +725,8 @@ Block/Cross-Axis Alignment: the 'align-self' property</h3>
 	The <dfn value for="align-self">auto</dfn> keyword computes to
 	itself on absolutely-positioned elements,
 	and to the computed value of 'align-items' on the parent
-	(minus any ''legacy'' keywords) on all other boxes.
+	(minus any ''legacy'' keywords) on all other boxes,
+	or ''start'' if the box has no parent.
 
 	<hr>
 

css-align/Overview.html

@@ -1274,7 +1274,8 @@ <h3 class="heading settled" data-level="5.1" id="justify-self-property"><span cl
       <p>The <dfn class="css" data-dfn-for="justify-self" data-dfn-type="value" data-export="" id="valdef-justify-self-auto">auto<a class="self-link" href="#valdef-justify-self-auto"></a></dfn> keyword computes to
 	itself on absolutely-positioned elements,
 	and to the computed value of <a class="property" data-link-type="propdesc" href="#propdef-justify-items">justify-items</a> on the parent
-	(minus any <a class="css" data-link-type="maybe" href="#valdef-justify-items-legacy">legacy</a> keywords) on all other boxes.</p>
+	(minus any <a class="css" data-link-type="maybe" href="#valdef-justify-items-legacy">legacy</a> keywords) on all other boxes,
+	or <a class="css" data-link-type="maybe" href="#valdef-item-position-content-position-start">start</a> if the box has no parent.</p>
 
 
 
@@ -1447,7 +1448,8 @@ <h3 class="heading settled" data-level="5.2" id="align-self-property"><span clas
       <p>The <dfn class="css" data-dfn-for="align-self" data-dfn-type="value" data-export="" id="valdef-align-self-auto">auto<a class="self-link" href="#valdef-align-self-auto"></a></dfn> keyword computes to
 	itself on absolutely-positioned elements,
 	and to the computed value of <a class="property" data-link-type="propdesc" href="#propdef-align-items">align-items</a> on the parent
-	(minus any <a class="css" data-link-type="maybe" href="#valdef-justify-items-legacy">legacy</a> keywords) on all other boxes.</p>
+	(minus any <a class="css" data-link-type="maybe" href="#valdef-justify-items-legacy">legacy</a> keywords) on all other boxes,
+	or <a class="css" data-link-type="maybe" href="#valdef-item-position-content-position-start">start</a> if the box has no parent.</p>