Define adding the ::view-transition

Author: jakearchibald

css-view-transitions-1/Overview.bs

@@ -259,6 +259,8 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
 		a [=pseudo-element parent=].
 		Its [=originating element=] is the document's [=document element=].
 
+		Its [=containing block=] is the [=snapshot viewport=].
+
 		The following is added to the [=HTML user agent style sheet=]:
 
 		```css
@@ -422,8 +424,6 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
 
 	- The [=view-transition layer=] paints after the stacking context for the [=document element=] and [=top layer=].
 
-	- The [=view-transition layer=]'s [=containing block=] is the [=snapshot viewport=].
-
 	Note: The intent of the feature is to be able to capture the contents of the page, which includes the top layer elements.
 	In order to accomplish that, the [=view-transition layer=] cannot be a part of the captured top layer context,
 	since that results in a circular dependency.
@@ -500,6 +500,16 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
 			Note: This is used to hold dynamic styles relating to transitions.
 	</dl>
 
+## Additions to [=document element=] ## {#additions-to-document-element}
+
+	A [=document element=] additionally has a <dfn for="document element">view-transition root pseudo-element</dfn>.
+	A ''::view-transition'' or null. Initially null.
+
+	When this is a ''::view-transition'', the ''::view-transition'' renders as a child of the [=document element=],
+	and the [=document element=] is its [=originating element=].
+
+	Note: The position of the ''::view-transition'' within the [=document element=] does not matter, as the ''::view-transition'''s [=containing block=] is the [=snapshot viewport=].
+
 # API # {#api}
 
 ## Additions to {{Document}} ## {#additions-to-document-api}
@@ -1054,7 +1064,7 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
 
 		1. Let |document| be [=this's=] [=relevant global object's=] [=associated document=].
 
-		1. [=list/Append=] |transition|'s [=ViewTransition/transition root pseudo-element=] to this |document|'s [=snapshot viewport=]'s [=pseudo-element parent/children=].
+		1. Set |document|'s [=document element=]'s [=view-transition root pseudo-element=] to |transition|'s [=ViewTransition/transition root pseudo-element=].
 
 		1. [=map/For each=] |transitionName| → |capturedElement| of |transition|'s [=ViewTransition/named elements=]:
 
@@ -1281,8 +1291,7 @@ urlPrefix: https://html.spec.whatwg.org/multipage/rendering.html; type: dfn;
 
 		1. Let |document| be |transition|'s [=relevant global object's=] [=associated document=].
 
-		1. [=list/Remove=] |transition|'s [=ViewTransition/transition root pseudo-element=]
-			from |document|'s [=snapshot viewport=]'s [=pseudo-element parent/children=].
+		1. Set |document|'s [=document element=]'s [=view-transition root pseudo-element=] to null.
 
 		1. [=list/For each=] |capturedElement| of |transition|'s [=ViewTransition/named elements=]' [=map/values=]: