HTML Checking for Large Sites

Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.

The label element may only contain one labelable descendant.

For example:

<label for="age">
  Age
  <select id="age">
    <option>young</option>
    <option>old</option>
  </select>
</label>

Learn more:

Related W3C validator issues