title: Hapi/Joi Validation: How to process text to a specific format
body: <p>Is it possible to pass a string to hapi/joi and for it to process it and return a required format? For example consider the code below:</p>
  <pre><code>const acceptedCitiesSchema = Joi.object({
      isCapitalCity: Joi.boolean().default(true),
      cityName: Joi.string().valid('MyCity', 'YourCity').required(),
  })
  </code></pre>
  <p>How can I make it that even if a user inputs <code>'myCity'</code> or <code>'yourCity'</code> joi automatically converts them to a format that the first word is capitalized(<code>'MyCity'</code> and <code>'YourCity'</code> respecively). And returns the desired results? Is it possible to achieve this using hapi/joi?</p>