Patch #1601678: move intern() to sys.intern().
diff --git a/Doc/lib/libsys.tex b/Doc/lib/libsys.tex
index 702427a..7a8859b 100644
--- a/Doc/lib/libsys.tex
+++ b/Doc/lib/libsys.tex
@@ -340,6 +340,21 @@
\versionadded{1.5.2}
\end{datadesc}
+\begin{funcdesc}{intern}{string}
+ Enter \var{string} in the table of ``interned'' strings and return
+ the interned string -- which is \var{string} itself or a copy.
+ Interning strings is useful to gain a little performance on
+ dictionary lookup -- if the keys in a dictionary are interned, and
+ the lookup key is interned, the key comparisons (after hashing) can
+ be done by a pointer compare instead of a string compare. Normally,
+ the names used in Python programs are automatically interned, and
+ the dictionaries used to hold module, class or instance attributes
+ have interned keys. \versionchanged[Interned strings are not
+ immortal (like they used to be in Python 2.2 and before);
+ you must keep a reference to the return value of \function{intern()}
+ around to benefit from it]{2.3}
+\end{funcdesc}
+
\begin{datadesc}{last_type}
\dataline{last_value}
\dataline{last_traceback}