Document the built-in iter() function.
diff --git a/Doc/lib/libfuncs.tex b/Doc/lib/libfuncs.tex
index d74abf6..c56d452 100644
--- a/Doc/lib/libfuncs.tex
+++ b/Doc/lib/libfuncs.tex
@@ -390,6 +390,23 @@
raised.
\end{funcdesc}
+\begin{funcdesc}{iter}{o\optional{, sentinel}}
+ Return an iterator object. The first argument is interpreted very
+ differently depending on the presence of the second argument.
+ Without a second argument, \var{o} must be a collection object which
+ supports the iteration protocol (the \method{__iter__()} method), or
+ it must support the sequence protocol (the \method{__getitem__()}
+ method with integer arguments starting at \code{0}). If it does not
+ support either of those protocols, \exception{TypeError} is raised.
+ If the second argument, \var{sentinel}, is given, then \var{o} must
+ be a callable object. The iterator created in this case will call
+ \var{o} with no arguments for each call to its \method{next()}
+ method; if the value returned is equal to \var{sentinel},
+ \exception{StopIteration} will be raised, otherwise the value will
+ be returned.
+ \versionadded{2.2}
+\end{funcdesc}
+
\begin{funcdesc}{len}{s}
Return the length (the number of items) of an object. The argument
may be a sequence (string, tuple or list) or a mapping (dictionary).