Ammended minor documentation detail abour Unicode cases.

src/libstd_unicode/char.rs

@@ -829,7 +829,8 @@ pub fn is_numeric(self) -> bool {
     /// // Sometimes the result is more than one character:
     /// assert_eq!('İ'.to_lowercase().to_string(), "i\u{307}");
     ///
-    /// // Japanese kanji characters do not have case, and so:
+    /// // Characters that do not have both uppercase and lowercase
+    /// // convert into themselves.
     /// assert_eq!('山'.to_lowercase().to_string(), "山");
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -889,7 +890,8 @@ pub fn to_lowercase(self) -> ToLowercase {
     /// // Sometimes the result is more than one character:
     /// assert_eq!('ß'.to_uppercase().to_string(), "SS");
     ///
-    /// // Japanese kanji characters do not have case, and so:
+    /// // Characters that do not have both uppercase and lowercase
+    /// // convert into themselves.
     /// assert_eq!('山'.to_uppercase().to_string(), "山");
     /// ```
     ///