diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 3357532..9bf522c 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -629,21 +629,27 @@ function _theme_build_registry($theme, $base_theme, $theme_engine) {
  *   An associative array of the currently available themes. The keys are the
  *   names of the themes and the values are objects having the following
  *   properties:
- *   - 'filename': The name of the .info file.
- *   - 'name': The machine name of the theme.
- *   - 'status': 1 for enabled, 0 for disabled themes.
- *   - 'info': The contents of the .info file.
- *   - 'stylesheets': A two dimensional array, using the first key for the
- *     'media' attribute (e.g. 'all'), the second for the name of the file
- *     (e.g. style.css). The value is a complete filepath
+ *   - filename: The name of the .info file.
+ *   - name: The machine name of the theme.
+ *   - status: 1 for enabled, 0 for disabled themes.
+ *   - info: The contents of the .info file.
+ *   - stylesheets: A two dimensional array, using the first key for the
+ *     media attribute (e.g. 'all'), the second for the name of the file
+ *     (e.g. style.css). The value is a complete filepath. Not set if no
+ *     stylesheets are defined in the .info file
  *     (e.g. themes/bartik/style.css).
- *   - 'scripts': An associative array of JavaScripts, using the filename as key
- *     and the complete filepath as value.
- *   - 'engine': The name of the theme engine.
- *   - 'base_theme': The name of the base theme.
- *   - 'base_themes': An ordered array of all the base themes. If the first item
- *     is NULL, a base theme is missing for this theme.
- *   - 'sub_themes': An unordered array of sub-themes of this theme.
+ *   - scripts: An associative array of JavaScripts, using the filename as key
+ *     and the complete filepath as value. Not set if no scripts are defined in
+ *     the .info file.
+ *   - prefix: Defined in the theme's engine nameprefix.
+ *   - engine: The name of the theme engine.
+ *   - base_theme: If this is a subtheme, the name of base theme. Otherwise
+ *     not set.
+ *   - base_themes: An ordered array of all the base themes. If the first item
+ *     is NULL, a base theme is missing for this theme. Not set if no base
+ *     themes are present.
+ *   - sub_themes: If the theme has sub-themes, an unordered array of
+ *     sub-themes. Otherwise key is unset.
  */
 function list_themes($refresh = FALSE) {
   $list = &drupal_static(__FUNCTION__, array());