title: Define options for type with PropTypes
body: <p>Is there a way to define multiple options (to serve as an internal overview / guide) when using <code>PropTypes</code>, as a companion for <code>defaultProps</code>?</p>
  <p>I usually just add comments to serve as an overview of the possible options, but is there a better way?
  E.g. when I have a button that can take different size (props) arguments such as <code>standard</code>, <code>large</code>, <code>subtle</code>, <code>fitToContent</code>, ...</p>
  <p><em>As a sidenote / side question — I want / need to learn TypeScript, is this something that can be done with TS?</em></p>