drupal/modules/upload/upload.js

// $Id$

(function ($) {

Drupal.behaviors.uploadFieldsetSummaries = {
  attach: function (context) {
    $('fieldset#edit-attachments', context).setSummary(function (context) {
      var size = $('#upload-attachments tbody tr').size();
      return Drupal.formatPlural(size, '1 attachment', '@count attachments');
    });
  }
};

})(jQuery);