JSFiddle - React, Tailwind, and code Playground

HTML

<form action="http://stackoverflow.com/questions/40968098/how-to-allow-only-letters-in-a-symfony2-form-in-twig">
      <label>Only letters: <input type="text" pattern="[a-zA-Z]*"></label>
      <input type="submit" value="Save" />
    </form>