Here’s a simple address group:

piklist('field', array(
  'type'    => 'group',
  'field'   => 'address',
  'template'=> 'field',
  'fields'  => array(
    array(
      'type'    => 'text',
      'field'   => 'street',
      'label'   => 'Street Address',
      'columns' => 12
    ),
    array(
      'type'    => 'text',
      'field'   => 'city',
      'label'   => 'City',
      'columns' => 4
    ),
    array(
      'type'    => 'select',
      'field'   => 'state',
      'label'   => 'State',
      'choices' => $states,
      'columns' => 4
    ),
    array(
      'type'    => 'text',
      'field'   => 'zip',
      'label'   => 'Zip Code',
      'columns' => 4,
      'validate'=> array(
        'type'    => 'zip-code'
      )
    )
  )
));

The code for the zip-code type can be found here: https://github.com/JasonTheAdams/PiklistHelper/blob/master/PiklistHelper.php#L88

I have had issues with validations in the past being finicky — in that they don’t always work. I’m not sure if something was changed that broke my old code, but the docs don’t seem to have changed.