diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 36c8228..3a9369c 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -629,21 +629,33 @@ 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
- *     (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.
+ *   - 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 (e.g.
+ *     themes/bartik/style.css). Not set if no stylesheets are defined in the
+ *     .info file.
+ *   - 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: The base theme engine prefix.
+ *   - engine: The name of the theme engine.
+ *   - base_theme: If this is a subtheme, the name of the base theme defined in
+ *     the .info file. Otherwise, the element is not set.
+ *   - base_themes: If this is a subtheme, a hierarchical associative array of
+ *     the base themes. This is not set if there are no base themes. Each theme
+ *     is an array key and the theme's name from the .info file is the value.
+ *     The key's value is NULL for a missing base theme. Additionally, array
+ *     elements are not set for any parents above the missing base theme.
+ *   - sub_themes: An unordered array of themes which define this theme as a
+ *     base theme in their .info files. Each array key is a subtheme and the
+ *     value is the theme's name from the theme's .info file. If a subtheme is
+ *     missing, the subtheme's key and all children of the subtheme will be
+ *     missing, even if the children exist in the filesystem. This element is
+ *     not set if there are no subthemes or if the base theme is missing.
  */
 function list_themes($refresh = FALSE) {
   $list = &drupal_static(__FUNCTION__, array());