diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 782b562..a00ba2a 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1197,14 +1197,33 @@ function theme($hook, $variables = array()) {
 }
 
 /**
- * Returns the path to the current themed element.
- *
- * It can point to the active theme or the module handling a themed
- * implementation. For example, when invoked within the scope of a theming call
- * it will depend on where the theming function is handled. If implemented from
- * a module, it will point to the module. If implemented from the active theme,
- * it will point to the active theme. When called outside the scope of a
- * theming call, it will always point to the active theme.
+ * Returns a path to the theme or module with the current theming function.
+ *
+ * This function usually returns the path to a "theming function". The meaning
+ * of "theming function" depends on whether the theme() call is using a theme
+ * function or a theme template.
+ *
+ * In calls to theme() that result in a theme function being used, the theme
+ * function that is actually called is the "theming function". So, this could be
+ * a theme_HOOK() reference implementation from a module, a THEME_HOOK()
+ * override from a base theme or the active theme, or a more specific override
+ * from a template suggestion, such as THEME_HOOK__type1().
+ *
+ * In calls to theme() that result in a template file being used, the "theming
+ * function" is the process or preprocess function that is called to set up the
+ * variables (with precidence given to the process function, if one exists). So,
+ * the "theming function" could be the template_process_HOOK() reference
+ * implementation from a module, a THEME_process_HOOK() override from a base
+ * theme or the active theme, etc. Note that the "theming function" may not be
+ * part of the same theme that contains the template file being used for
+ * theming in this case.
+ *
+ * @return
+ *   Outside of the scope of a call to theme(), this function returns the path
+ *   to the default theme, or to the custom theme for the current page. Within
+ *   the scope of a call to theme(), this function returns the path to the
+ *   module or theme containing the "theming function" (see above) that is
+ *   called for the element being themed.
  */
 function path_to_theme() {
   global $theme_path;