...
  ## Uncomment this code to see an example of how you can easily add a field to the registration page
  ## NOTE: In order to save the favorite color in the "doAfterRegistration" hook, this page must be
  ## saved by an administrator and can not self sandboxing.
  #set($sandbox = false)
  #set($field =
    {'name' : 'favorite_color',
      'label' : 'What is your favorite color',
      'params' : {
        'type' : 'text',
        'size' : '60'
      },
      'validate' : {
        'mandatory' : {
          'failureMessage' : $services.localization.render('core.validation.required.message')
        },
        'regex' : {
          'pattern' : '/^green$/',
          'failureMessage' : 'You are not cool enough to register here.'
        },
        'fieldOkayMessage' : 'You are awesome.'
      },
      'doAfterRegistration' : '#saveFavoriteColor()'
    })
  #set($discard = $fields.add($field))
  ## Save the user's favorite color on their user page.
  #macro(saveFavoriteColor)
    #set($xwikiname = $request.get('xwikiname'))
    #set($userDoc = $xwiki.getDocument("$userSpace$xwikiname"))
    $userDoc.setContent("$userDoc.getContent() ${xwikiname}'s favorite color is $request.get('favorite_color')!")
    ## The user (who is not yet logged in) can't save documents so saveWithProgrammingRights
    ## will save the document as long as the user who last saved this registration page has programming rights.
    $userDoc.saveWithProgrammingRights("Saved favorite color from registration form.")
  #end
...