title: What happens when a XHTML DOCTYPE doesn't validate?
body: <p>Life is good, using XHTML Strict with much success</p>
  
  <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"&gt;
  </code></pre>
  
  <p>...Then, bam! You toss a Vimeo video onto your page that breaks validation.</p>
  
  <pre><code>&lt;iframe src="http://player.vimeo.com/video/XXXXX?byline=0&amp;amp;portrait=0" width="468" height="351" frameborder="0"&gt;&lt;/iframe&gt;
  </code></pre>
  
  <p>No iframes allowed, sir!</p>
  
  <p>So, what impact does it have on the way the page renders, or impact on the visitor? Why care about the validation of this iframe?</p>