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─────Run-Time Library───────────────────────────────────────────────────────
 
     The _tzset function uses the current setting of the environment
     variable TZ to assign values to three global variables: _daylight,
     _timezone, and _tzname. These variables are used by the _ftime and
     localtime functions to make corrections from Universal Coordinated
     Time (UCT) to local time, and by the time function to compute UCT
     from system time.
 
     Use the following syntax to set the TZ environment variable:
 
          set TZ=tzn[+│-]hh[:mm[:ss]][dzn]
 
     The <tzn> argument must be a three-letter time-zone name, such as
     PST, followed by an optionally signed number, [+│-]<hh>, giving
     the difference in hours between UCT and local time. The hours can
     be optionally followed by minutes, :<mm>; seconds, :<ss>; and a
     three-letter daylight-saving-time (DST) zone, such as PDT. For
     example, PST8PDT represents a valid TZ value for the Pacific time
     zone.
 
     Separate hours, minutes, and seconds with colons (:). If DST is
     never in effect, as is the case in certain states and localities,
     TZ should be set without a <dzn> zone.
 
     If TZ is not currently set, the default is PST8PDT, which
     corresponds to the Pacific time zone.
 
     Based on the TZ environment variable, the following values are
     assigned to the _daylight, _timezone, and _tzname variables when
     _tzset is called:
 
     Variable      Value
 
     _daylight     Nonzero value if a daylight-saving-time zone is
                   specified in the TZ setting; otherwise, 0
 
     _timezone     The difference in seconds between UCT and local time
 
     _tzname[0]    The string value of the three-letter time-zone name
                   from the TZ setting
 
     _tzname[1]    The string value of the daylight-saving-time zone,
                   or an empty string if the daylight-saving-time
                   zone is omitted from the TZ setting
 
     The default for _daylight is 1; for _timezone, 28800; for
     _tzname[0], PST; and for _tzname[1], PDT. This corresponds to
     PST8PDT.
 
     If the DST zone is omitted from the TZ settings, the _daylight
     variable will be 0 and the _ftime, gmtime, and localtime functions
     will return 0 for their DST flags.
 
     Return Value
 
     None.
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