Index: includes/common.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/common.inc,v
retrieving revision 1.756.2.98
diff -u -r1.756.2.98 common.inc
--- includes/common.inc	6 Sep 2010 11:13:27 -0000	1.756.2.98
+++ includes/common.inc	1 Nov 2010 15:35:40 -0000
@@ -2842,13 +2842,23 @@
  * interface for all altering operations.
  *
  * @param $type
- *   The data type of the structured array. 'form', 'links',
- *   'node_content', and so on are several examples.
+ *   A string describing the type of the alterable $data. 'form', 'links',
+ *   'node_content', and so on are several examples. Alternatively can be an
+ *   array, in which case hook_TYPE_alter() is invoked for each value in the
+ *   array, ordered first by module, and then for each module, in the order of
+ *   values in $type. For example, when Form API is using drupal_alter() to
+ *   execute both hook_form_alter() and hook_form_FORM_ID_alter()
+ *   implementations, it passes array('form', 'form_' . $form_id) for $type.
  * @param $data
- *   The structured array to be altered.
+ *   The variable that will be passed to hook_TYPE_alter() implementations to be
+ *   altered. The type of this variable depends on $type. For example, when
+ *   altering a 'form', $data will be a structured array. When altering a
+ *   'profile', $data will be an object.
  * @param ...
- *   Any additional params will be passed on to the called
- *   hook_$type_alter functions.
+ *   In case more arguments need to be passed and alterable, modules may provide
+ *   additional variables by using an array containing the index
+ *   '__drupal_alter_by_ref' to pass two by-reference arguments to the
+ *   hook implementation.
  */
 function drupal_alter($type, &$data) {
   // PHP's func_get_args() always returns copies of params, not references, so