diff --git includes/form.inc includes/form.inc
index 5f61ef8..bcc39fc 100644
--- includes/form.inc
+++ includes/form.inc
@@ -147,6 +147,17 @@
  *   the 'values' array exclusively. The most common use of this key is for
  *   multi-step forms that need to clear some of the user input when setting
  *   'rebuild'.
+ * - 'build_info': An array holding the information needed to build the form.
+ *   The 'args' key contains an array of arguments that are used to rebuild the
+ *   form from cache; e.g., in case of an AJAX request. After initial creation
+ *   the content of the 'args' key is read-only.
+ *   The 'files' key under 'build_info' contains an array of include files that
+ *   need to be loaded when the form is built, whereas each array entry may be
+ *   the path to a file or another array containing values for the parameters
+ *   'type', 'module' and 'name' as needed by module_load_include(). Modules may
+ *   add further include files to this array; e.g. this could be used by a
+ *   module to make sure an include file containing handlers added by the module
+ *   are loaded.
  */
 
 /**