diff -u b/modules/system/system.module b/modules/system/system.module
--- b/modules/system/system.module
+++ b/modules/system/system.module
@@ -2706,13 +2706,14 @@
  *   Possible values: REGIONS_ALL or REGIONS_VISIBLE. Visible excludes hidden
  *   regions.
  * @param bool $labels
- *   (Optional) boolean to specify whether the human readable machine names
- *   should be returned or not, defaults to TRUE, but can be set to FALSE by
- *   calling code if it only needs machine names.
+ *   (optional) Boolean to specify whether the human readable machine names
+ *   should be returned or not. Defaults to TRUE, but calling code can set
+ *   this to FALSE for better performance, if it only needs machine names.
  *
  * @return array
  *   An associative array of regions in the form $region['name'] = 'description'
- *   or $region['name'] = 'name', if $labels is set to FALSE.
+ *   if $labels is set to TRUE, or $region['name'] = 'name', if $labels is set
+ *   to FALSE.
  */
 function system_region_list($theme_key, $show = REGIONS_ALL, $labels = TRUE) {
   $themes = list_themes();