From 7c9253c7b3026f2519f01f117bca35c8e9205342 Mon Sep 17 00:00:00 2001 From: Paul Eggert Date: Mon, 16 Jan 2017 15:53:45 -0800 Subject: [PROPOSED] Document preferences for historical abbreviations (Problems reported by Michael Deckers.) * NEWS, Theory: Document this. --- NEWS | 3 +++ Theory | 13 +++++++++++++ 2 files changed, 16 insertions(+) diff --git a/NEWS b/NEWS index 3975295..900ccbb 100644 --- a/NEWS +++ b/NEWS @@ -80,6 +80,9 @@ Unreleased, experimental changes Changes to documentation and commentary + The 'Theory' file now better documents choice of historical time + zone abbreviations. (Problems reported by Michael Deckers.) + tz-link.htm now covers leap smearing, which is popular in clouds. diff --git a/Theory b/Theory index 533ee93..33e4606 100644 --- a/Theory +++ b/Theory @@ -209,6 +209,19 @@ in decreasing order of importance: If there is no common English abbreviation, use numeric offsets like -05 and +0830 that are generated by zic's %z notation. + Use current abbreviations for older timestamps to avoid confusion. + For example, in 1910 a common English abbreviation for UT +01 + in central Europe was 'MEZ' (short for both "Middle European + Zone" and for "Mitteleuropäische Zeit" in German). Nowadays + 'CET' ("Central European Time") is more common in English, and + the database uses 'CET' even for circa-1910 timestamps as this + is less confusing for modern users and avoids the need for + determining when 'CET' supplanted 'MEZ' in common usage. + + Use a consistent style in a zone's history. For example, if a zone's + history tends to use numeric abbreviations and a particular + entry could go either way, use a numeric abbreviation. + [The remaining guidelines predate the introduction of %z. They are problematic as they mean tz data entries invent notation rather than record it. These guidelines are now -- 2.7.4