Hello, See my message to the documentation list about where to document everything ajax, ahax, js, and jquery. http://drupal.org/node/121997 Right now, I am trying hard to understand book.js and ... I just don't get it. In book.js, there is an ajax call: $.ajax({ url: Drupal.settings.book.formCallback +'/'+ $('#'+ Drupal.settings.book.formId +' input[name=form_build_id]').val() +'/'+ $('#edit-book-bid').val(), dataType: 'json', success: function(data) { // Insert the new select, and remove the progress bar. $('#edit-book-plid-wrapper').after(data['book']).remove(); } in book_menu(), there is a menu callback, which I guess is the callback used by the js above: $items['book/js/form'] = array( 'page callback' => 'book_form_update', 'access arguments' => array('access content'), 'type' => MENU_CALLBACK, 'file' => 'book.pages.inc', ); But everything javascript and ajax being completely undocumented, I am having a hard time to connect the two together, even by looking at drupal.js, looking at the big documentation block above drupal_add_js() (in common.inc), which I don't understand at all (I told you it was too early to change my handle!!) How does this... $.ajax({ url: Drupal.settings.book.formCallback +'/'+ $('#'+ Drupal.settings.book.formId +' input[name=form_build_id]').val()+'/'+ $('#edit-book-bid').val(), ...lead to the book/js/form callback??? I sense it is connected to Drupal.attachBehaviors (in drupal.js) and Drupal.behaviors.bookSelect (book.js), but I don't know how. As I always do, if you tell me both the answer and where to document this, I'll have a go at starting a documentation. Thanks and blessings, Augustin.