title: Custom validators in WTForms using Flask
body: <p>I need to make a custom validator in WTForms where the input is to be: <em>number</em>:<em>number</em> - e.g. 2:1</p>
  
  <pre><code>match1 = StringField('Russia-Saudi Arabia', validators=[DataRequired()])
  </code></pre>
  
  <p>So, my question is - how to create such validator?</p>
  
  <p>I've looked upon the documentation at <a href="http://wtforms.readthedocs.io/en/latest/validators.html" rel="noreferrer">http://wtforms.readthedocs.io/en/latest/validators.html</a>, but was not very helpful (for me) in this case. </p>
  
  <p>Thanks in advance</p>