diff --git a/source b/source
index b99a3a21c71..c6005bb1f76 100644
--- a/source
+++ b/source
@@ -78098,11 +78098,18 @@ interface <dfn data-export="" data-dfn-type="interface">Window</dfn> : <span>Eve
   void <span data-x="dom-window-cancelAnimationFrame">cancelAnimationFrame</span>(unsigned long handle);
 
   void <span data-x="dom-window-postMessage">postMessage</span>(any message, USVString targetOrigin, optional sequence&lt;<span data-x="idl-object">object</span>&gt; transfer = []);
+  void <span data-x="dom-window-postMessage">postMessage</span>(any message, optional sequence&lt;<span data-x="idl-object">object</span>&gt; transfer = [], optional <span>WindowPostMessageOptions</span> options);
 };
 <span>Window</span> includes <span>GlobalEventHandlers</span>;
 <span>Window</span> includes <span>WindowEventHandlers</span>;
 
-callback <dfn>FrameRequestCallback</dfn> = void (<span>DOMHighResTimeStamp</span> time);</pre>
+callback <dfn>FrameRequestCallback</dfn> = void (<span>DOMHighResTimeStamp</span> time);
+
+dictionary <dfn>WindowPostMessageOptions</dfn>
+{
+  USVString targetOrigin = "/";
+};
+</pre>
 
 <!-- for more features to add here, look here:
  http://msdn.microsoft.com/workshop/author/dhtml/reference/objects/obj_window.asp
@@ -95379,10 +95386,9 @@ function receiver(e) {
 
   <dl class="domintro">
 
-   <dt><var>window</var> . <code subdfn data-x="dom-window-postMessage">postMessage</code>(<var>message</var>, <var>targetOrigin</var> [, <var>transfer</var> ] )</dt>
+   <dt><var>window</var> . <code subdfn data-x="dom-window-postMessage">postMessage</code>(<var>message</var>[, <var>transfer</var> ] [, options ])</dt>
 
    <dd>
-
     <p>Posts a message to the given window. Messages can be structured objects, e.g. nested objects
     and arrays, can contain JavaScript values (strings, numbers, <code>Date</code>
     objects, etc), and can contain certain data objects such as <code>File</code> <code>Blob</code>,
@@ -95391,6 +95397,9 @@ function receiver(e) {
     <p>Objects listed in <var>transfer</var> are transferred, not just cloned, meaning that
     they are no longer usable on the sending side.</p>
 
+    <p>Target origin is specified as a member of <var>options</var>. If options is not provided
+    targetOrigin of the dictionary is initialized to "<code data-x="">/</code>".</p>
+
     <p>If the origin of the target window doesn't match the given origin, the message is discarded,
     to avoid information leakage. To send the message to the target regardless of origin, set the
     target origin to "<code data-x="">*</code>". To restrict the message to same-origin targets only,
@@ -95402,6 +95411,15 @@ function receiver(e) {
     cloned.</p>
 
    </dd>
+   <dt><var>window</var> . <code data-x="dom-window-postMessage">postMessage</code>(<var>message</var>, <var>targetOrigin</var> [, <var>transfer</var> ] )</dt>
+
+   <dd>
+
+    <p>This is an alternate version of postMessage where the target origin is specified as a parameter.
+    Calling <code data-x="">window.postMessage(message, target, transfer);</code> is equivalent
+    to <code data-x="">window.postMessage(message, transfer, {targetOrigin: target});</code>
+
+   </dd>
 
   </dl>
 
@@ -95417,7 +95435,7 @@ function receiver(e) {
   <div w-nodev>
 
   <p>The <dfn><code data-x="dom-window-postMessage">postMessage(<var>message</var>,
-  <var>targetOrigin</var>, <var>transfer</var>)</code></dfn> method, when invoked on a
+  <var>transfer</var>, <var>options</var>)</code></dfn> method, when invoked on a
   <code>Window</code> object must run the following steps:</p>
 
   <ol> <!-- a lot of this is similar or identical to port.postMessage -->
@@ -95433,6 +95451,8 @@ function receiver(e) {
    window, in same-origin cases. See discussion at
    https://github.com/whatwg/html/issues/1542#issuecomment-233502636 -->
 
+   <li><p>Let <var>targetOrigin</var> be <var>options</var>'s targetOrigin.</p></li>
+
    <li><p>If <var>targetOrigin</var> is a single U+002F SOLIDUS character (/), then set
    <var>targetOrigin</var> to <var>incumbentSettings</var>'s <span
    data-x="concept-settings-object-origin">origin</span>.</p>