title: a Django URLField has fixed max_length as 200 characters
body: <pre><code>link = models.URLField(max_length=500, blank=True, default='')
  </code></pre>
  
  <p>I have already set the max_length as 500, but every time I tried to set this field with url larger than 200 characters, it still threw an error saying that <code>Ensure this value has at most 200 characters (it has 327).</code> Is this a Django restriction or something I forgot to set up?</p>