- documented Ellipsis, NotImplemented

- minor markup changes
- indented for consistency with newer content

Doc/lib/libconsts.tex

-\section{Builtin Constants}
+\section{Built-in Constants}
 
-A small number of constants live in the builtin namespace.  They are:
+A small number of constants live in the built-in namespace.  They are:
 
 \begin{datadesc}{False}
-The false value of the \code{bool} type.
-\versionadded{2.3}
+  The false value of the \class{bool} type.
+  \versionadded{2.3}
 \end{datadesc}
 
 \begin{datadesc}{True}
-The true value of the \code{bool} type.
-\versionadded{2.3}
+  The true value of the \class{bool} type.
+  \versionadded{2.3}
 \end{datadesc}
 
 \begin{datadesc}{None}
-The sole value of \code{NoneType}.  \code{None} is frequently used to
-represent the absence of a value, as when default arguments are not passed
-to a function.
+  The sole value of \code{\refmodule{types}.NoneType}.  \code{None} is
+  frequently used to represent the absence of a value, as when default
+  arguments are not passed to a function.
 \end{datadesc}
 
+\begin{datadesc}{NotImplemented}
+  Special value which can be returned by the ``rich comparison''
+  special methods (\method{__eq__()}, \method{__lt__()}, and friends),
+  to indicate that the comparison is not implemented with respect to
+  the other type.
+\end{datadesc}
+
+\begin{datadesc}{Ellipsis}
+  Special value used in conjunction with extended slicing syntax.
+  % XXX Someone who understands extended slicing should fill in here.
+\end{datadesc}