Where does the VCALENDAR DTSTART come from?

[edalzell]

This code:

use Spatie\IcalendarGenerator\Components\Calendar;
use Spatie\IcalendarGenerator\Components\Event;

Calendar::create('Laracon online')
    ->event(Event::create('Creating calender feeds')
        ->startsAt(new DateTime('6 March 2019 15:00'))
        ->endsAt(new DateTime('6 March 2019 16:00'))
    )
    ->get();

Produces this text:

   BEGIN:VCALENDAR\r\n
   VERSION:2.0\r\n
   PRODID:spatie/icalendar-generator\r\n
   NAME:Laracon online\r\n
   X-WR-CALNAME:Laracon online\r\n
   BEGIN:VTIMEZONE\r\n
   TZID:America/Los_Angeles\r\n
   BEGIN:DAYLIGHT\r\n
   DTSTART:20180609T160000\r\n
   TZOFFSETFROM:-0700\r\n
   TZOFFSETTO:-0700\r\n
   END:DAYLIGHT\r\n
   END:VTIMEZONE\r\n
   BEGIN:VTIMEZONE\r\n
   TZID:UTC\r\n
   BEGIN:STANDARD\r\n
   DTSTART:20210719T192201\r\n
   TZOFFSETFROM:+0000\r\n
   TZOFFSETTO:+0000\r\n
   END:STANDARD\r\n
   END:VTIMEZONE\r\n
   BEGIN:VEVENT\r\n
   UID:6259c5d9f251f\r\n
   DTSTAMP:20220415T192201Z\r\n
   SUMMARY:Creating calender feeds\r\n
   DTSTART;TZID=America/Los_Angeles:20190306T150000\r\n
   DTEND;TZID=America/Los_Angeles:20190306T160000\r\n
   END:VEVENT\r\n
   END:VCALENDAR

Where does the DTSTART:20180609T160000 come from?

[rubenvanassche]

The package will automatically try to figure out timezones for all dates within your calendar. These are determined here:

icalendar-generator/src/Timezones/TimezoneTransitionsResolver.php

Line 12 in ce4525d

class TimezoneTransitionsResolver