How should I use hook_field_extra_fields()? I just found out about hook_field_extra_fields(), but the documentation doesn't really tell me how to use it.

Where is the extra-fields output generated?

I tried hard to understand the Node and Poll modules, but I can't figure it out. I also tried to add a custom field formatter.
This is a simple example showing how to add an additional field to the Field UI and provides an example of one way of inserting the field onto a node.

/**
 * Implements hook_field_extra_fields().
 */
function MODULE_field_extra_fields() {
  $extra['node']['article']['display']['extended_submitted_by'] = array(
    'label' =&gt; t('Extended Submitted By'),
    'description' =&gt; t('Provides Jumper Menu for Version Selection'),
    'weight' =&gt; 0,
  );
  return $extra;
}

/**
 * Implements hook_node_view().
 */
function MODULE_node_view($node, $view_mode, $langcode) {
  // Only add if the view mode is for a full view, although we 
  // could control this via the Field UI too using 'hidden'.
  if ($view_mode == 'full' &amp;&amp; $node-&gt;type == 'article') {
    $node-&gt;content['extended_submitted_by'] = array(
      '#markup' =&gt; '&lt;p&gt;This is inserted unless hidden in the field ui.&lt;/p&gt;',
    );
  }
}