diff --git a/core/includes/form.inc b/core/includes/form.inc
index 665a9e6..b1934af 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -3709,6 +3709,36 @@ function theme_vertical_tabs($variables) {
  *   The form element to process. Properties used:
  *   - #autocomplete_path: A system path to be used as callback URL by the
  *     autocomplete JavaScript library.
+ *
+ * * Here is an example of how to use an autocompletion callback:
+ *
+ * Autocomplete callback functions tend to have a bug wherein forward-slash
+ * characters cause an error.
+ *
+ * If the request has a '/' in the text, then the menu system will split it
+ * into multiple arguments and recover the intended $keywords.
+ *
+ * If your autocomplete path in the menu is 'mymodule_autocomplete' and in
+ * your form you have:
+ *
+ * @code
+ * '#autocomplete_path' => 'mymodule_autocomplete/' . $some_key . '/' . $some_id,
+ * @endcode
+ *
+ * and the user types in "keywords" so the full path called is:
+ *
+ * 'mymodule_autocomplete/$some_key/$some_id/keywords'.
+ *
+ * @code
+ * function mymodule_autocomplete_callback($arg1, $arg2, $keywords) {
+ *   $args = func_get_args();
+ *   array_shift($args);
+ *   array_shift($args);
+ *   $keywords = implode('/', $args);
+ *
+ *   // Your code here.
+ * }
+ * @endcode
  */
 function form_process_autocomplete($element, &$form_state) {
   if (!empty($element['#autocomplete_path']) && drupal_valid_path($element['#autocomplete_path'])) {