Is this the proper way to add a 'class' attribute to a form date element $form['stop_date'] = array(
  '#type' =&gt; 'date',
  '#title' =&gt; t('Stop Date'),
  '#default_value' =&gt; date("Y-m-d"), // default to today 
  '#id' =&gt; 'stop_date', 
  '#attributes' =&gt; array('class' =&gt; array('dateSel-Fld')), 
  '#required' =&gt; true,
);


When using the #attribute property the form is not being rendered successfully.
Yep.

Here's the references:

https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7#attributes

And a usage example:

https://api.drupal.org/api/drupal/modules!search!search.module/7