title: How is the onreadystatechange event supported everywhere but document.readyState isn't?
body: <p>According to MDN <a href="https://developer.mozilla.org/en-US/docs/Web/API/Document/readystatechange_event" rel="nofollow noreferrer">here</a> and <a href="https://developer.mozilla.org/en-US/docs/Web/API/Document/readyState" rel="nofollow noreferrer">here</a>, it says that the <code>readystatechange</code> event is supported in all browsers, but the <code>document.readyState</code> property is only supported back until around IE9+ (8*).</p>
  
  <p>This doesn't really make sense, given that literal definition of the <code>readystatechange</code> event is: </p>
  
  <p><em>The readystatechange event is fired when the readyState attribute of a document has changed.</em></p>
  
  <p>Unless previous implementations of <code>readystatechange</code> keep <code>document.readyState</code> as an internal variable that can't be accessed. Is this the case, or is this simply a documentation error?</p>