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adttz = acauema's date time timezone — a single line stamp carrying date, 24h clock, and place, so no stamp ever floats in an ambiguous "when". the avi slot takes aviation codes (iata airport codes, lowercase): the zone a time lives in, never "tz", never a bare offset.

format

2026 10 13 t 15 30 waw
yyyy mm dd t hhmm avi

yyyymmdd — calendar date, zero-padded
t — separator; acauema's own stamps write it as d: 20261013d1111waw (cixt headers). both accepted
hhmm — 24h clock, zero-padded
avi — aviation (iata) code for the zone the time is in: waw warsaw, lhr london, lis lisbon, jfk new york, hnd tokyo

examples — same instant, five cities

20261013t1530waw   15:30 warsaw (CEST, utc+2 summer)
20261013t1430lhr   14:30 london, Europe/London local (BST, utc+1 summer)
20261013t0930jfk    9:30 new york (EDT)
20261013t2230hnd   22:30 tokyo (JST)

20261013d1111waw   acauema's own stamp style: 11:11 warsaw, 2026-10-13

rules

never stamp without the avi code. "14:50" alone = dunno which reality.
24h only. euro-locale numbers.
local means local: london time is lhr with Europe/London semantics (BST/GMT by season) — never relabelled utc.
sharing across zones: convert, or stamp both — the reader never does math.
filenames and logs love it: sorts with sort, greppable, no punctuation to escape.

law lives in cixt (#iso). page born 20261013t1600waw.