diff --git a/source b/source
index 6d394fe07a4..c66343dd29c 100644
--- a/source
+++ b/source
@@ -25588,6 +25588,11 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
       undefined.</p>
      </dd>
     </dl>
+
+    <p class="note">Animated images will become <span data-x="img-all">completely available</span>
+    only after all their frames are loaded. Thus, even though an implementation could decode the
+    first frame before that point, the above steps will not do so, instead waiting until all frames
+    are available.</p>
    </li>
 
    <li><p>Return <var>promise</var>.</p></li>