title: How exactly am I to format this a-zA-Z for GROK custom regular expressions?
body: <p>Please see image. How the heck do you get a simple [a-zA-Z] expression to work in the KIBANA X-Pack Grok debugger?
  I've tried several flavors and have ran the regex just fine in normal regex testing environments where it finds all that I need but this debugger wants something that I cannot figure out. Again this is a CUSTOM regular expression not the pre-built ones.</p>
  
  <p><a href="https://i.stack.imgur.com/d0nXy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/d0nXy.png" alt="screenshot"></a></p>
  
  <ul>
  <li>[a-z]</li>
  <li>[A-Z]</li>
  <li>[a-zA-Z]</li>
  <li>([a-zA-Z]+)</li>
  </ul>
  
  <p>and more</p>