Specify element.activeViewTransition. (#13130)

Author: skobes-chromium

css-view-transitions-2/Overview.bs

@@ -1628,7 +1628,9 @@ the [=active view transition=] is exposed to script via a document property.
 		or null if there is no active view transition.
 </dl>
 
-Issue: Is this updated by a <code>rootEl.startViewTransition()</code> call, too?
+Note: An <code>element.startViewTransition()</code> call does not update
+<code>document.activeViewTransition</code>, but will update
+{{Element/activeViewTransition}} on the <code>element</code>.
 
 ## Additions to {{Element}} ## {#additions-to-element-api}
 
@@ -1710,6 +1712,17 @@ Issue: Is this updated by a <code>rootEl.startViewTransition()</code> call, too?
 		1. Return |viewTransition|.
 	</div>
 
+### {{Element/activeViewTransition}} Property ### {#element-activeviewtransition}
+
+Similar to [Document.activeViewTransition](#doc-activeviewtransition),
+the active view transition of an element is exposed to script via a property on the element.
+
+<dl dfn-type=attribute dfn-for=Element>
+	: <dfn>activeViewTransition</dfn>
+	:: Returns the [=active view transition=] for the [=element=],
+		or null if there is no active view transition.
+</dl>
+
 ## The {{ViewTransition}} interface ## {#the-domtransition-interface}
 
 	<xmp class=idl>