title: What are the allowed characters in a subdomain?
body: <p>What characters are you allowed to use in a subdomain?</p>
  
  <p>Example: for <code>someSub.example.com</code> the <code>someSub</code> portion. </p>
  
  <p>I know you can use letters, numbers, and hyphens, but what about other characters? Can <code>_</code> (underscore) be used? </p>