diff --git a/index.html b/index.html
index 6351c5c..8bea1e1 100644
--- a/index.html
+++ b/index.html
@@ -3469,9 +3469,16 @@ <h5 id="idl-wheeleventinit">WheelEventInit</h5>
 				double deltaY = 0.0;
 				double deltaZ = 0.0;
 				unsigned long deltaMode = 0;
+				boolean momentum = false;
 			};
 			</pre>
 
+			<p class="issue">
+				The definitions below seem redundant when we already have the corresponding
+				attributes defined above. See
+				<a href="https://github.com/w3c/pointerevents/issues/646">pointerevents/646</a>.
+			</p>
+		
 			<dl data-dfn-for="WheelEventInit">
 				<dt><dfn>deltaX</dfn></dt>
 				<dd>See <code>deltaZ</code> attribute.</dd>
@@ -3501,6 +3508,11 @@ <h5 id="idl-wheeleventinit">WheelEventInit</h5>
 					({{WheelEvent/DOM_DELTA_PAGE}}) if the <a>rotation</a> of the
 					wheel would have resulted in scrolling.
 				</dd>
+
+				<dt><dfn>momentum</dfn></dt>
+				<dd>
+					Initializes the {{WheelEvent/momentum}} attribute.
+				</dd>
 			</dl>
 
 	<h4 id="events-wheel-types">Wheel Event Types</h4>