title: Form required attribute validation error
body: <p>I'm trying to put the final touches on a site that I'm building and I'm coming up with a validation error that I can't figure out. It involves the use of the "required" attribute in one of my forms. Here is the form code:</p>
  
  <pre><code>&lt;div id="sub"&gt;
      &lt;form id="subForm" action="MAILTO:tworley1977@yahoo.com" method="post" enctype="text/plain"&gt;
          &lt;label class="floatLabel" for="subBox"&gt;&lt;b&gt;ENTER YOUR EMAIL IN THE BOX BELOW TO SUBSCRIBE TO OUR NEWSLETTER&lt;/b&gt;&lt;/label&gt; &lt;br/&gt;
          &lt;input type="text" name="subBox" id="subBox" size="20" required /&gt; &lt;br/&gt;
      &lt;fieldset id="buttons"&gt;
          &lt;input type="submit" value="Subscribe" /&gt;
          &lt;input type="reset" value="Cancel" /&gt;
      &lt;/fieldset&gt;
      &lt;/form&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I'm using a transitional doctype.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8" ?&gt;
  
  &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
  
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
  </code></pre>
  
  <p>Checking with W3C Markup Validator; this is the error that keeps coming up:</p>
  
  <p>Line 116, Column 69: "required" is not a member of a group specified for any attribute</p>
  
  <pre><code>        &lt;input type="text" name="subBox" id="subBox" size="20" required /&gt; &lt;br/&gt;
  </code></pre>
  
  <p>This is the only error that I'm getting, but as near as I can tell, I'm using the required attribute correctly. It renders correctly in the browser and works as expected.</p>
  
  <p>Any thoughts as to why I'm getting this validation error??
  Thanks.</p>