Document ERR and OK

Doc/lib/libcurses.tex

@@ -1026,6 +1026,17 @@ length \var{n} consisting of the character \var{ch}.
 
 The \module{curses} module defines the following data members:
 
+\begin{datadesc}{ERR}
+Some curses routines  that  return  an integer, such as 
+\function{getch()}, return ERR upon failure.  
+\end{datadesc}
+
+\begin{datadesc}{OK}
+Some curses routines  that  return  an integer, such as 
+\function{napms()}, return OK upon success.  
+
+\end{datadesc}
+
 \begin{datadesc}{version}
 A string representing the current version of the module. 
 Also available as \constant{__version__}.