diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index aa558b2..a162ea4 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -406,10 +406,14 @@ function drupal_find_base_themes($themes, $key) {
  * @link themeable theme function or template @endlink, by checking the theme
  * registry.
  *
- * Avoid calling this function directly. It is preferable to replace direct
- * calls to the _theme() function with calls to drupal_render() by passing a
- * render array with a #theme key to drupal_render(), which in turn calls
- * _theme().
+ * Do not call this function directly as it will prevent the following items 
+ * from working correctly:
+ * - Caching.
+ * - JavaScript and CSS asset attachment.
+ * - Pre / post render hooks.
+ * - Defaults provided by hook_element_info(), including attached assets.
+ * Instead, build a render array with a #theme key, and either return the
+ * array (where possible) or call drupal_render() to convert it to HTML.
  *
  * @section sec_theme_hooks Theme Hooks
  * Most commonly, the first argument to this function is the name of the theme