title: evaluateJavaScript in a WKWebView's iframe?
body: <p>I have successfully set up a WKWebView ScriptMessageHandler to receive messages from inside my webview. I'm then using <code>evaluateJavaScript</code> to send responses back into the webview. This works fine when everything is executed on the main frame of the view.</p>
  
  <p>However, when I try to do this inside an iFrame I run into difficulties. I still receive the message in the message handler (complete with <code>WKFrameInfo</code> to tell me where it came from) but I can't find any way to run <code>evalateJavaScript</code> targeting that frame. I <em>could</em> use a <code>window.frames</code> hack in my evaluated JavaScript, but if the iFrame is of a different origin than the parent frame then I'm going to run into cross-domain errors.</p>
  
  <p>Is there any way to identify a frame inside WKWebview, and evaluate JS on it?</p>