<div dir="ltr">Ok. Thanks for explaining. I think I get it, and the summary of my understanding is that:<div><br></div><div>The zone.tab will have fewer zones than zone1970.tab when to represent the pre-1970 / zone.tab rules it would require the synthesis of a new zone ID purely to represent the < 1970 situation.</div><div><br></div><div>i.e. in the case of TF and Indian/Reunion, Indian/Reunion can be used for TF after 1970 but it would not be correct before 1970, and there is no existing candidate that would be.</div><div><br></div><div>Thanks!</div><div><br></div><div><div>Neil.<br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On 31 March 2017 at 21:03, Paul Eggert <span dir="ltr"><<a href="mailto:eggert@cs.ucla.edu" target="_blank">eggert@cs.ucla.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">Neil Fuller via tz wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I expect the exact zone IDs to be different, but there are only a few cases<br>
where countries differ in the number of referenced zone IDs.<br>
</blockquote>
<br></span>
These discrepancies come up because zone.tab tries to be compatible with the old tz rules, whereas the rest of the data follow the new rules (and zone1970.tab reflects the new rules). The old rules weren't as well documented, I'm afraid, so this is a bit of a murky area.<span class=""><br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I realize that zone.tab is intended for backward compatibility but it looks<br>
like it is being well maintained.<br>
</blockquote>
<br></span>
Yes, zone.tab is still quite commonly used. How long this will continue to be true is anybody's guess. Perhaps until the next political crisis....<span class=""><br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
zone.tab:<br>
<br>
TF -492110+0701303 Indian/Kerguelen<br>
<br>
zone1970.tab:<br>
<br>
RE,TF -2052+05528 Indian/Reunion Réunion, Crozet, Scattered Islands<br>
TF -492110+0701303 Indian/Kerguelen Kerguelen, St Paul Island, Amsterdam<br>
Island<br>
</blockquote>
<br></span>
In theory according to the old rules, there should be two zones for TF: the existing one and another zone for Crozet and the Scattered Islands. The new rules say that we don't need the latter zone, as it's identical to Indian/Reunion since 1970. (And thank goodness! hardly anyone lives on Crozet etc., and info about civil time there is hard to come by.)<br>
<br>
zone.tab approximates the old rules with the new data as best it can. It doesn't use Indian/Reunion under TF as I expect consumers of zone.tab expect zone.tab to be a 1-1 relation.<span class=""><br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
zone.tab:<br>
<br>
UM +2813-17722 Pacific/Midway Midway Islands<br>
UM +1917+16637 Pacific/Wake Wake Island<br>
<br>
zone1970.tab:<br>
<br>
AS,UM -1416-17042 Pacific/Pago_Pago Samoa, Midway<br>
UM +1917+16637 Pacific/Wake Wake Island<br>
US,UM +211825-1575130 Pacific/Honolulu Hawaii<br>
</blockquote>
<br></span>
The Pacific/Honolulu link is to UM as Indian/Reunion is to TF. That is, it stands for minor islands that would need a separate zone under the old rules, but not for the new ones. Johnston Island comes to mind.<br>
<br>
Pacific/Midway is an old-fashioned alias for Pacific/Pago_Pago, so zone.tab uses it to preserve the illusion that it's 1-1. It can't do this for TF and Indian/Reunion as the latter has no aliases. We don't create aliases merely to do minor cleanups of zone.tab for backward-compatibility purposes.<span class=""><br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
zone.tab:<br>
<br>
VN +1045+10640 Asia/Ho_Chi_Minh<br>
<br>
zone1970.tab:<br>
<br>
TH,KH,LA,VN +1345+10031 Asia/Bangkok Indochina (most areas)<br>
VN +1045+10640 Asia/Ho_Chi_Minh Vietnam (south)<br>
</blockquote>
<br></span>
Asia/Bangkok is to VN as Indian/Reunion is to TF. It stands for part of Vietnam that would need a separate zone under the old rules, but not the new ones. The region in question is the old North Vietnam. It has no aliases, so zone.tab doesn't use it under VN.<br>
</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>Google UK Limited<br><br>Registered Office: 6 Pancras Square, London, N1C 4AG<br>Registered in England Number: 3977902</div></div></div></div></div>
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