Added more cross-references.
diff --git a/Doc/library/stringio.rst b/Doc/library/stringio.rst
index 9e2f0da..4736fc3 100644
--- a/Doc/library/stringio.rst
+++ b/Doc/library/stringio.rst
@@ -8,7 +8,8 @@
This module implements a file-like class, :class:`StringIO`, that reads and
writes a string buffer (also known as *memory files*). See the description of
-file objects for operations (section :ref:`bltin-file-objects`).
+file objects for operations (section :ref:`bltin-file-objects`). (For
+standard strings, see :class:`str` and :class:`unicode`.)
.. class:: StringIO([buffer])