diff --git includes/form.inc includes/form.inc
index c0812bb..fb17541 100644
--- includes/form.inc
+++ includes/form.inc
@@ -126,6 +126,14 @@
  *   which may or may not be a button (in the case of AJAX forms.) This is
  *   often used to distinguish between various buttons in a submit handler,
  *   and is also used in AJAX handlers.
+ * - wrapper_callback: Modules that wish to pre-populate certain forms with
+ *   common elements, such as back/next/save buttons in multi-step form
+ *   wizards, may define a form builder function name that returns a form
+ *   structure, which is passed on to the actual form builder function.
+ *   Such implementations may either define the 'wrapper_callback' via
+ *   hook_forms() or have to invoke drupal_build_form() (instead of
+ *   drupal_get_form()) on their own in a custom menu callback to prepare
+ *   $form_state accordingly. See drupal_build_form().
  * - 'cache': The typical form workflow involves two page requests. During the
  *   first page request, a form is built and returned for the user to fill in.
  *   Then the user fills the form in and submits it, triggering a second page