ffdn.org/sites/all/modules/footnotes/footnotes_field/footnotes_field.module

<?php

/**
 * @file
 * Hooks and general logic for the Footnotes field module.
 */

/**
 * Implements hook_ctools_plugin_api().
 */
function footnotes_field_ctools_plugin_api($module, $api) {
  if (($module == 'ds' && $api == 'ds') || ($module == 'ds_extras' && $api == 'ds_extras')) {
    return array('version' => 1);
  }
}

/**
 * Implements hook_menu().
 */
function footnotes_field_menu() {
  $items['admin/config/content/footnotes'] = array(
    'title' => 'Footnotes',
    'description' => 'Config page for footnotes fields/blocks',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('_footnotes_field_admin_form'),
    'access arguments' => array('administer footnotes fields'),
    'file' => 'includes/footnotes_field.admin.inc',
  );

  return $items;
}

/**
 * Implements hook_permission().
 */
function footnotes_field_permission() {
  return array(
    'administer footnotes fields' => array(
      'title' => t('Administer footnotes fields'),
      'description' => t('Perform administration tasks for footnotes fields.'),
    ),
  );
}

/**
 * Implements hook_ds_fields_info().
 */
function footnotes_field_ds_fields_info($entity_type) {
  $fields = array();
  $settings = _footnotes_field_get_settings();

  if (!empty($settings['content_types'])) {
    $content_types = array_keys(array_filter($settings['content_types']));
    // Only expose this field if there is at least one content type selected.
    if (!empty($content_types)) {
      $ui_limit = array();
      foreach ($content_types as $content_type) {
        $ui_limit[] = $content_type . '|*';
      }

      $fields['footnotes_field'] = array(
        'title' => t('Footnotes (ds field)'),
        'field_type' => DS_FIELD_TYPE_FUNCTION,
        'ui_limit' => $ui_limit,
        'file' => drupal_get_path('module', 'footnotes_field') . '/ds/ds_footnotes_ui_field.inc',
        'function' => '_footnotes_field_render',
        'properties' => array(),
      );

      return array('node' => $fields);
    }
  }
}

/**
 * Implements hook_block_info().
 */
function footnotes_field_block_info() {
  $blocks['footnotes'] = array(
    'info' => t('Footnotes: node detail'),
  );
  return $blocks;
}

/**
 * Implements hook_block_view().
 */
function footnotes_field_block_view($delta = '') {
  $block = array();
  switch ($delta) {
    case 'footnotes':
      $node = menu_get_object('node');
      $settings = _footnotes_field_get_settings();

      if ($node && !empty($settings['expose_block'])) {
        $block['subject'] = t('Footnotes');
        $block['content'] = array(
          '#prefix' => '<div id="footnotes-all">',
          '#markup' => NULL,
          '#suffix' => '</div>',
          '#attached' => array(
            'js' => array(
              array(
                'data' => drupal_get_path('module', 'footnotes_field') . '/js/footnotes_field.js',
                'type' => 'file',
              ),
            ),
            'css' => array(
              array(
                'data' => drupal_get_path('module', 'footnotes_field') . '/css/footnotes_field.css',
                'type' => 'file',
              ),
            ),
          ),
        );
        break;
      }
  }
  return $block;
}

/**
 * Fetches settings form admin page.
 *
 * @return array
 *   The footnotes field settings.
 */
function _footnotes_field_get_settings() {
  return variable_get('footnotes_field_settings', array());
}