title: Filter out and lower case all characters using onKeyDown (ev: React.KeyboardEvent<HTMLElement>)
body: <p>I am using the <a href="https://developer.microsoft.com/en-us/fabric#/controls/web/pickers" rel="nofollow noreferrer"><code>TagPicker</code></a> which has the event <code>onKeyDown</code> with signature <code>(ev: React.KeyboardEvent&lt;HTMLElement&gt;) =&gt; void</code></p>
  
  <p>Is there a way I can use this event to only allow lower-case letters and the dash <code>-</code> symbol? Ideally I would like to transform upper-case letters to lower-case automatically. </p>