SF #735051, add time.tzset documentation
diff --git a/Doc/lib/libtime.tex b/Doc/lib/libtime.tex
index a6a2e73..5f838cf 100644
--- a/Doc/lib/libtime.tex
+++ b/Doc/lib/libtime.tex
@@ -324,6 +324,102 @@
timezone is defined, the second string should not be used.
\end{datadesc}
+\begin{funcdesc}{tzset}{}
+Resets the time conversion rules used by the library routines.
+The environment variable \envvar{TZ} specifies how this is done.
+\versionadded{2.3}
+
+Availability: \UNIX.
+
+\begin{notice}
+Although in many cases, changing the \envvar{TZ} environment variable
+may affect the output of functions like \function{localtime} without calling
+\function{tzset}, this behavior should not be relied on.
+
+The \envvar{TZ} environment variable should contain no whitespace.
+\end{notice}
+
+The standard format of the \envvar{TZ} environment variable is:
+(whitespace added for clarity)
+\begin{itemize}
+ \item[std offset [dst [offset] [,start[/time], end[/time]]]]
+\end{itemize}
+
+Where:
+
+\begin{itemize}
+ \item[std and dst]
+ Three or more alphanumerics giving the timezone abbreviations.
+ These will be propogated into time.tzname
+
+ \item[offset]
+ The offset has the form: \plusminus hh[:mm[:ss]].
+ This indicates the value added the local time to arrive at UTC.
+ If preceded by a '-', the timezone is east of the Prime
+ Meridian; otherwise, it is west. If no offset follows
+ dst, summmer time is assumed to be one hour ahead of standard time.
+
+ \item[start[/time],end[/time]]
+ Indicates when to change to and back from DST. The format of the
+ start and end dates are one of the following:
+
+ \begin{itemize}
+ \item[J\var{n}]
+ The Julian day \var{n} (1 <= \var{n} <= 365). Leap days are not
+ counted, so in all years February 28 is day 59 and
+ March 1 is day 60.
+
+ \item[\var{n}]
+ The zero-based Julian day (0 <= \var{n} <= 365). Leap days are
+ counted, and it is possible to refer to February 29.
+
+ \item[M\var{m}.\var{n}.\var{d}]
+ The \var{d}'th day (0 <= \var{d} <= 6) or week \var{n}
+ of month \var{m} of the year (1 <= \var{n} <= 5,
+ 1 <= \var{m} <= 12, where week 5 means "the last \var{d} day
+ in month \var{m}" which may occur in either the fourth or
+ the fifth week). Week 1 is the first week in which the
+ \var{d}'th day occurs. Day zero is Sunday.
+ \end{itemize}
+
+ time has the same format as offset except that no leading sign ('-' or
+ '+') is allowed. The default, if time is not given, is 02:00:00.
+\end{itemize}
+
+
+\begin{verbatim}
+>>> os.environ['TZ'] = 'EST+05EDT,M4.1.0,M10.5.0'
+>>> time.tzset()
+>>> time.strftime('%X %x %Z')
+'02:07:36 05/08/03 EDT'
+>>> os.environ['TZ'] = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
+>>> time.tzset()
+>>> time.strftime('%X %x %Z')
+'16:08:12 05/08/03 AEST'
+\end{verbatim}
+
+On many Unix systems (including *BSD, Linux, Solaris, and Darwin), it
+is more convenient to use the system's zoneinfo (\manpage{tzfile}{5})
+database to specify the timezone rules. To do this, set the
+\envvar{TZ} environment variable to the path of the required timezone
+datafile, relative to the root of the systems 'zoneinfo' timezone database,
+usually located at \file{/usr/share/zoneinfo}. For example,
+\code{'US/Eastern'}, \code{'Australia/Melbourne'}, \code{'Egypt'} or
+\code{'Europe/Amsterdam'}.
+
+\begin{verbatim}
+>>> os.environ['TZ'] = 'US/Eastern'
+>>> time.tzset()
+>>> time.tzname
+('EST', 'EDT')
+>>> os.environ['TZ'] = 'Egypt'
+>>> time.tzset()
+>>> time.tzname
+('EET', 'EEST')
+\end{verbatim}
+
+\end{funcdesc}
+
\begin{seealso}
\seemodule{locale}{Internationalization services. The locale