SF bug #872461: list.extend() described as experimental

Doc/lib/libstdtypes.tex

@@ -1013,9 +1013,7 @@ Notes:
   no longer works in Python 2.0.  Use of this misfeature has been
   deprecated since Python 1.4.
 
-\item[(3)] Raises an exception when \var{x} is not a list object.  The
-  \method{extend()} method is experimental and not supported by
-  mutable sequence types other than lists.
+\item[(3)] Raises an exception when \var{x} is not a list object.
 
 \item[(4)] Raises \exception{ValueError} when \var{x} is not found in
   \var{s}. When a negative index is passed as the second or third parameter