1Timezone strings: 2----------------- 3This is a description of valid timezone strings for ENV[ARC]:TZ: 4"XPG3TZ - time zone information" 5The form of the time zone information is based on the XPG3 specification of 6the TZ environment variable. Spaces are allowed only in timezone 7designations, where they are significant. The following description 8closely follows the XPG3 specification, except for the paragraphs starting 9**CLARIFICATION**. 10 11<std><offset>[<dst>[<offset>],<start>[/<time>],<end>[/<time>]] 12 13Where: 14<std> and <dst> 15 Are each three or more bytes that are the designation for the 16 standard (<std>) and daylight savings time (<dst>) timezones. 17 Only <std> is required - if <dst> is missing, then daylight 18 savings time does not apply in this locale. Upper- and 19 lower-case letters are allowed. Any characters except a 20 leading colon (:), digits, a comma (,), a minus (-) or a plus 21 (+) are allowed. 22 **CLARIFICATION** The two-byte designation `UT' is permitted. 23<offset> 24 Indicates the value one must add to the local time to arrive 25 at Coordinated Universal Time. The offset has the form: 26 <hh>[:<mm>[:<ss>]] 27 The minutes <mm> and seconds <ss> are optional. The hour <hh> 28 is required and may be a single digit. The offset following 29 <std> is required. If no offset follows <dst>, daylight savings 30 time is assumed to be one hour ahead of standard time. One or 31 more digits may be used; the value is always interpreted as a 32 decimal number. The hour must be between 0 and 24, and the 33 minutes (and seconds) if present between 0 and 59. Out of 34 range values may cause unpredictable behavior. If preceded by 35 a `-', the timezone is east of the Prime Meridian; otherwise 36 it is west (which may be indicated by an optional preceding 37 `+' sign). 38 **CLARIFICATION** No more than two digits are allowed in any 39 of <hh>, <mm> or <ss>. Leading zeros are permitted. 40<start>/<time> and <end>/<time> 41 Indicates when to change to and back from daylight savings 42 time, where <start>/<time> describes when the change from 43 standard time to daylight savings time occurs, and 44 <end>/<time> describes when the change back happens. Each 45 <time> field describes when, in current local time, the change 46 is made. 47 **CLARIFICATION** It is recognized that in the Southern 48 hemisphere <start> will specify a date later than <end>. 49 The formats of <start> and <end> are one of the following: 50 J<n> The Julian day <n> (1 <= <n> <= 365). Leap days are not 51 counted. That is, in all years, February 28 is day 59 52 and March 1 is day 60. It is impossible to refer to 53 the occasional February 29. 54 <n> The zero-based Julian day (0 <= <n> <= 365). Leap days 55 are counted, and it is possible to refer to February 56 29. 57 M<m>.<n>.<d> 58 The <d>th day, (0 <= <d> <= 6) of week <n> of month <m> 59 of the year (1 <= <n> <= 5, 1 <= <m> <= 12), where week 60 5 means `the last <d>-day in month <m>' (which may 61 occur in either the fourth or the fifth week). Week 1 62 is the first week in which the <d>th day occurs. Day 63 zero is Sunday. 64 **CLARIFICATION** Neither <n> nor <m> may have a 65 leading zero. <d> must be a single digit. 66 **CLARIFICATION** The default <start> and <end> values 67 are from the first Sunday in April until the last Sunday 68 in October. This allows United States users to leave out 69 the <start> and <end> parts, as most are accustomed to 70 doing. 71 <time> has the same format as <offset> except that no leading 72 sign (`-' or `+') is allowed. The default, if <time> is not 73 given is 02:00:00. 74 **CLARIFICATION** The number of hours in <time> may be up 75 to 167, to allow encoding of rules such as `00:00hrs on the 76 Sunday after the second Friday in September' 77 78Example (for Central Europe): 79----------------------------- 80MET-1MEST,M3.5.0,M10.5.0/03 81 82Another example, for the US East Coast: 83--------------------------------------- 84EST5EDT4,M4.1.0/02,M10.5.0/02 85This string describes the default values when no time zone is set. 86