title: Will HTML 5 validation be worth the candle?
body: <p>It's widely considered that the best reason to validate one's HTML is to ensure that all browsers will treat it consistently and predictably. </p>
  
  <p>The HTML 5 draft,  however, contains two specifications in one. First an author spec, describing the elements and attributes that HTML authors should use, and their interrelationships. Validation of an HTML 5 page is based on this spec. The elements and attributes included are not directly drawn from HTML 4, but have needed to be justified from first principles, which means that some HTML 4 features, such as the summary attribute on &lt;table&gt;, longdesc on &lt;img&gt; and the profile attribute on &lt;head&gt;, do not currently appear in this draft. Such features are not considered deprecated, they are simply not included. (Their absence from the draft remains a matter of dispute, although their inclusion any time soon does not seem likely.)</p>
  
  <p>Second, the draft defines a browser processing specification that seeks to define exactly how a browser's parser will treat any byte stream it's given, regardless of how well formed and valid the HTML. This means that when the browsers fully support HTML 5, it will be possible to predict how any browser will treat HTML for a much wider range of inputs than merely those that pass validation.</p>
  
  <p>In particular, because HTML 5 is defined to be 100% backward compatible with today's web, all valid HTML 4, and all invalid but commonly used mark-up, will continue to be processed exactly the same as it is today, regardless of whether it is HTML 5 valid or not.</p>
  
  <p>Therefore, at the very minimum, anyone using any feature from HTML 5, HTML 4, or any previous version of HTML, plus many proprietary extensions, can be confident that their HTML will get consistent and predictable treatment across all browsers.</p>
  
  <p>Given this, does it make any sense to limit ones HTML 5 to that which will validate, and what practical benefit will we get from doing so?</p>