title: html5 input datetime-local: optional time is possible?
body: <p>I have this input field </p>
  
  <pre><code>&lt;input type="datetime-local" required&gt;
  </code></pre>
  
  <p>I would like the date part to be always required, but not the time part...
  I tried with pattern, like</p>
  
  <pre><code>pattern="[0-9]{4}-[0-9]{2}-[0-9]{2}.*"
  </code></pre>
  
  <p>but it doesn't seem to work...
  any idea...</p>
  
  <p>Edit:
  I explain better here</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;form name="test" method="POST" action="/"&gt;
    &lt;input type="datetime-local" name="event_date_start" id="event_date_start"  
           min="2011-06-07T00:00" 
           max="2099-06-14T00:00" required&gt;&lt;br&gt;
    
    &lt;input type="submit"/&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>What I want is to use datetime, but time must be optional.
  With the above example, submit is not allowed until you insert 00 in the time field..</p>
  
  <p>I want to leave that optional...</p>