tito10047 / php-calendar / 28450041266

Pull #3

github

fix: preserve IANA timezones in ICalExporter, document timezone behaviour

Previously export() always serialised all datetimes as UTC (Z suffix),
silently dropping the original timezone. Recurring events from a parsed
ICS file with TZID=Europe/London would be written back at UTC time,
shifting them by the UTC offset.

New behaviour (formatDtProp helper):
  - UTC datetimes → DTSTART:20241101T120000Z (unchanged)
  - Named IANA timezone → DTSTART;TZID=Europe/London:20241101T120000
  - Numeric offset (+01:00) → normalised to UTC (offset info cannot be
    preserved without a VTIMEZONE block; document this limitation)

Update class docblock to document the three-case timezone strategy and
warn about the numeric-offset limitation so users know to pass a proper
DateTimeZone('Region/City') when timezone fidelity matters.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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