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(slib.info)Time Zone

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Time Zone
---------

  (require 'time-zone)

 - Data Format: TZ-string
     POSIX standards specify several formats for encoding time-zone
     rules.

    :<pathname>
          If the first character of <pathname> is `/', then <pathname>
          specifies the absolute pathname of a tzfile(5) format
          time-zone file.  Otherwise, <pathname> is interpreted as a
          pathname within TZFILE:VICINITY (/usr/lib/zoneinfo/) naming a
          tzfile(5) format time-zone file.

    <std><offset>
          The string <std> consists of 3 or more alphabetic characters.
          <offset> specifies the time difference from GMT.  The <offset>
          is positive if the local time zone is west of the Prime
          Meridian and negative if it is east.  <offset> can be the
          number of hours or hours and minutes (and optionally seconds)
          separated by `:'.  For example, `-4:30'.

    <std><offset><dst>
          <dst> is the at least 3 alphabetic characters naming the local
          daylight-savings-time.

    <std><offset><dst><doffset>
          <doffset> specifies the offset from the Prime Meridian when
          daylight-savings-time is in effect.

     The non-tzfile formats can optionally be followed by transition
     times specifying the day and time when a zone changes from
     standard to daylight-savings and back again.

    ,<date>/<time>,<date>/<time>
          The <time>s are specified like the <offset>s above, except
          that leading `+' and `-' are not allowed.

          Each <date> has one of the formats:

         J<day>
               specifies the Julian day with <day> between 1 and 365.
               February 29 is never counted and cannot be referenced.

         <day>
               This specifies the Julian day with n between 0 and 365.
               February 29 is counted in leap years and can be
               specified.

         M<month>.<week>.<day>
               This specifies day <day> (0 <= <day> <= 6) of week
               <week> (1 <= <week> <= 5) of month <month> (1 <= <month>
               <= 12).  Week 1 is the first week in which day d occurs
               and week 5 is the last week in which day <day> occurs.
               Day 0 is a Sunday.


 - Data Type: time-zone
     is a datatype encoding how many hours from Greenwich Mean Time the
     local time is, and the "Daylight Savings Time" rules for changing
     it.

 - Function: time-zone TZ-string
     Creates and returns a time-zone object specified by the string
     TZ-STRING.  If `time-zone' cannot interpret TZ-STRING, `#f' is
     returned.

 - Function: tz:params caltime tz
     TZ is a time-zone object.  `tz:params' returns a list of three
     items:
       0. An integer.  0 if standard time is in effect for timezone TZ
          at CALTIME; 1 if daylight savings time is in effect for
          timezone TZ at CALTIME.

       1. The number of seconds west of the Prime Meridian timezone TZ
          is at CALTIME.

       2. The name for timezone TZ at CALTIME.

     `tz:params' is unaffected by the default timezone; inquiries can be
     made of any timezone at any calendar time.


The rest of these procedures and variables are provided for POSIX
compatability.  Because of shared state they are not thread-safe.

 - Function: tzset
     Returns the default time-zone.

 - Function: tzset tz
     Sets (and returns) the default time-zone to TZ.

 - Function: tzset TZ-string
     Sets (and returns) the default time-zone to that specified by
     TZ-STRING.

     `tzset' also sets the variables *TIMEZONE*, DAYLIGHT?, and TZNAME.
     This function is automatically called by the time conversion
     procedures which depend on the time zone (Note: Time and Date).

 - Variable: *timezone*
     Contains the difference, in seconds, between Greenwich Mean Time
     and local standard time (for example, in the U.S.  Eastern time
     zone (EST), timezone is 5*60*60).  `*timezone*' is initialized by
     `tzset'.

 - Variable: daylight?
     is `#t' if the default timezone has rules for "Daylight Savings
     Time".  _Note:_ DAYLIGHT? does not tell you when Daylight Savings
     Time is in effect, just that the default zone sometimes has
     Daylight Savings Time.

 - Variable: tzname
     is a vector of strings.  Index 0 has the abbreviation for the
     standard timezone; If DAYLIGHT?, then index 1 has the abbreviation
     for the Daylight Savings timezone.