title: UIWebView producing about:blank requests when iframe appended
body: <p>This simple code</p>
  
  <p><code>var iframe = document.createElement('iframe');
  document.documentElement.appendChild(iframe);</code></p>
  
  <p>injected by <code>UIWebView stringByEvaluatingJavascriptFromString</code>
  produces invocation of <code>UIWebViewDelegate shouldStartLoadWithRequest</code> with <code>about:blank</code>. Which interestingly still has <code>mainDocumentURL</code> set to the document that was there at the time of injection. For me it means that i can't inject such code whenever i want - reentry to <code>shouldStartLoadWithRequest</code> observably breaks a lot of things. I can reject all <code>about:blank</code> requests (returning <code>NO</code> from <code>shouldStart...</code>) and code snippets from the internets do it cluelessly, but it's hardly a systematic solution.</p>
  
  <p>Any ideas why <code>UIWebView</code> has this confusing and useless behavior?</p>