title: What values for checked and selected are false?
body: <p>I think according to W3 spec, you're supposed to do</p>
  
  <pre><code>&lt;input type="checkbox" checked="checked" /&gt;
  </code></pre>
  
  <p>And</p>
  
  <pre><code> selected="selected"
  </code></pre>
  
  <p>But, most browsers will accept it you just write "CHECKED" and don't give it a value. So, what if you do include the attribute, are there any values that would be (consistently) considered false?</p>