-\begin{verbatim}
-Copyright 1992, 1993, 1994, 1997 Henry Spencer. All rights reserved.
-This software is not subject to any license of the American Telephone
-and Telegraph Company or of the Regents of the University of California.
-
-Permission is granted to anyone to use this software for any purpose on
-any computer system, and to alter it and redistribute it, subject
-to the following restrictions:
-
-1. The author is not responsible for the consequences of use of this
- software, no matter how awful, even if they arise from flaws in it.
+Regular expressions, as defined by POSIX, come in two flavours: {\it extended}
+and {\it basic}. The builtin library also adds a third flavour
+of expression \helpref{advanced}{wxresyn}, which is not available
+when using the system library.