title: Set WTForms submit button to icon
body: <p>I want a submit button that displays an icon rather than text.  The button is a field in a WTForms form.  I am using Bootstrap and Open Iconic for styling and icons.  How do I set the submit field to display an icon?</p>
  
  <pre><code>class MyForm(Form):
      submit = SubmitField('')
  </code></pre>
  
  
  
  <pre><code>{{ form.submit }}
  </code></pre>
  
  <p><a href="https://stackoverflow.com/questions/30668029/creating-a-form-with-a-varying-number-of-repeated-subform-in-flask-wtforms">This post</a> refers to an <code>icon</code> method, but I can't find any more information on it.</p>