abstract class boxes_box {
  static $boxes; // Static cache of box objects.
  public $delta;
  public $title;
  public $description;
  public $options;
  public $plugin_key;
  public $new;
  public $export_type;

  /**
   * Load existing box by its unique identifier $delta.
   */
  public static function load($delta, $reset = FALSE) {
    if (!isset(self::$boxes[$delta]) || $reset) {
      ctools_include('export');
      $box = ctools_export_load_object('box', 'names', array($delta));
      if (!empty($box) && $values = array_pop($box)) {
        self::$boxes[$delta] = self::factory($values->plugin_key, $values);
        self::$boxes[$delta]->new = FALSE;
      }
    }
    return isset(self::$boxes[$delta]) && get_class(self::$boxes[$delta]) != 'stdClass' ? self::$boxes[$delta] : NULL;
  }

  /**
   * Instantiate, populate and return a box object.
   *
   * @param $plugin_key
   *
   * @param $values
   *   An array with at least a plugin_key key identifying the plugin class to
   *   use for instantiating this box.
   */
  public static function factory($plugin_key, $values) {
    ctools_include('plugins');
    if ($class = ctools_plugin_load_class('boxes', 'plugins', $plugin_key, 'handler')) {

      // While we actually prefer to get objects, we need to allow for either,
      // so we convert it all to arrays.
      if (is_object($values)) {
        $values = (array) $values;
      }

      $box = new $class();
      $box->plugin_key = $plugin_key;

      foreach ($box as $key => $value) {
        if (isset($values[$key])) {
          $box->$key = $values[$key];
        }
      }
      foreach ($box->options_defaults() as $key => $value) {
        if (isset($values[$key])) {
          $box->options[$key] = $values[$key];
        }
      }
      return $box;
    }
    return FALSE;
  }

  /**
   * Create a new box.
   */
  protected function __construct() {
    $this->new = TRUE; // A box is new unless it exists in the DB or in code.
    $this->options = $this->options_defaults();
  }

  /**
   * Reset the boxes cache.
   *
   * Both ctools and boxes current maintain caches, ctools of the config and
   * boxes of the loaded box objects. We clear them both.
   */
  public static function reset() {
    ctools_include('export');
    ctools_export_load_object_reset('box');
    self::$boxes = array();
  }

  /**
   * Save a box.
   */
  public function save() {
    if (empty($this->delta)) {
      throw new Exception(t('Cannot save box without a specified delta.'));
    }
    self::reset();
    $existing = boxes_box_load($this->delta);
    if ($existing && ($existing->export_type & EXPORT_IN_DATABASE)) {
      drupal_write_record('box', $this, array('delta'));
    }
    else {
      drupal_write_record('box', $this);
    }
    $this->new = FALSE;
    self::reset();
    module_exists('context') ? context_invalidate_cache() : NULL;
  }

  /**
   * Delete a box.
   */
  public function delete() {
    self::reset();
    unset(self::$boxes[$this->delta]);
    db_delete('box')->condition('delta', $this->delta)->execute();
    module_exists('context') ? context_invalidate_cache() : NULL;
  }

  /**
   * Declare if the box should use a multistep form for the create form.
   *
   * This might me necessary for forms that use ajax on the options form.
   * Currently Context does not load this block correctly and the ajax in the
   * form will not work. Methinks Context UI Editor needs to be upgraded to
   * D7 AJAX framework for this to not be required. That said the functionality
   * is potentially useful even with proper functioning AJAX.
   */
  public function use_multistep_create() {
    return FALSE;
  }

  /**
   * Returns the block cache settings for this box. Subclasses can override this
   * to perform more intricate operations around deciding the cache settings of
   * the specific box instance.
   */
  public function cache_setting() {
    return DRUPAL_CACHE_CUSTOM;
  }

  /**
   * Declare default options.
   */
  abstract public function options_defaults();

  /**
   * Provide options to configure content.
   */
  abstract public function options_form(&$form_state);

  /**
   * Render a block. Must return an array with the keys
   * 'delta', 'title', 'subject' (same as title) and 'content'.
   *
   * title AND subject need to be present to avoid that block module overrides
   * title.
   */
  abstract public function render();
}

boxes_block_view in sites/all/modules/ulmus/boxes/boxes.module

Implements hook_block_view().

boxes_boxes_plugins in sites/all/modules/ulmus/boxes/boxes.module

Implements hook_boxes_plugins().

boxes_theme in sites/all/modules/ulmus/boxes/boxes.module

Implements hook_theme().