Draft
Birth time zones and daylight saving
Civil clock times need a zone; ambiguous or missing hours are handled explicitly.
Original draft for local preview. Human editorial review is still pending; this article is not published in production.
You enter a civil date, optional clock time, and IANA time zone. The server resolves UTC with the platform zone database.
When clocks fall back, the same local time can occur twice. You must choose the earlier or later occurrence, or ask the form to stop.
A skipped spring-forward hour cannot be used. Incomplete time stays incomplete; the product does not invent a missing hour.
A numeric offset such as UTC+8 describes one offset, while a named zone such as Asia/Shanghai supplies historical rules for the date. A birthplace label alone is not used to guess a time zone. Select the intended zone explicitly. The conversion should preserve the original civil input so you can later check how a UTC instant was obtained.
When a fall-back hour occurs twice, 'earlier' and 'later' select different instants even though the wall-clock text matches. If you cannot establish which occurrence was intended, stop or keep the birth time unknown. During a spring-forward gap, choosing a nearby valid hour would change the evidence and should not happen silently. A date without a time needs a range of possible instants; converting an invented noon would conceal uncertainty rather than resolve it.