title: Windows Store HTML app with popup window
body: <p>I'm wrapping a web app in a Windows Store app shell using a <code>x-ms-webview</code>. This works fine, but I have one problem. I use PayPal and since PayPal doesn't allow to be <code>iframed</code> I need to open PayPal in a new browser window.</p>
  
  <p>On regular browsers this isn't a problem. The window open and when the user returns from PayPal I can a callback on "<code>opener</code>" and update the users account.</p>
  
  <p>But when doing this in a Windows Store app the <code>window.open</code> triggers IE to launch. The problem is to return to my app and let it know that the user finished the transaction.</p>
  
  <p>My first idea was just to use a <code>URI activation</code>. This kind of works, but I having trouble knowing if the PayPal page was launch from a regular browser or an app. I also think it is confusing for the user to be taken to another app to make the purchase.</p>
  
  <p>I would prefer to have the window open in my app, but I'm not sure how I would open open a new <code>x-ms-webview</code> as a modal window overlapping existing webview. </p>
  
  <p>What is the best way to communicate from the current web view and the app? 
  Can I use <code>postMessage</code> to send messages between the app and the <code>x-ms-webview</code> even though the src of the web view is a http hosted site?</p>
  
  <p>Thank you for your help.</p>