Event-Time-Zone-Implementation-Planning.md

@@ -35,6 +35,8 @@ The start and end dates have traditionally provided the _nominal perspective_ (*
 * It provides backward-compatibility for [relevant screens/tools/APIs](#affected) -- by returning the start and end dates in the same way. (_If you call `Event.get +w id=4 +s start_date` in v5.30 and v5.60, you should get the same value._)
 * Screens may be updated incrementally to give richer information (using any of the columns, depending on the downstream goals+preferences).
 
+Note that "universal time" is based on current projections but DST rules may vary in the future, so since the nominal date/time/timezone is authoritative, the universal time may need to be re-calculated.  (See [examples](https://www.vertabelo.com/blog/the-proper-way-to-handle-multiple-time-zones-in-mysql/#does%20this%20data%20represent%20a%20point%20in%20time%20in%20the%20past%20or%20in%20the%20future?).)
+
 Changes required to support timezones:
 
 1. Addition of DATETIME columns to hold the GMT date & time for indexed sorting:
@@ -54,7 +56,7 @@ Changes required to support timezones:
 6. An additional token to show the event timezone †
 7. Changes to various system workflow message to display timezone information with event messages †
 8. Additional fields to the API to show the event timezone †
-
+9. Process to re-calculate universal times after timezone rule changes.
 
 † Already implemented in original PR
 
@@ -158,6 +160,12 @@ Sorted by `Status,Environment`:
 | :question: | Pantheon | Needs testing/clarification. | 
 | :question: | WP Engine | Needs testing/clarification. |
 
+## Other reading
+
+- First attempt at introducing timezones for events (V1 above): https://lab.civicrm.org/dev/core/-/issues/2122
+- Useful reading (linked in above PR): ["Today I learned about MySQL and timezones"](https://javorszky.co.uk/2016/06/06/today-i-learned-about-mysql-and-timezones/), ["The Proper Way to Handle Multiple Time Zones in MySQL"](https://www.vertabelo.com/blog/the-proper-way-to-handle-multiple-time-zones-in-mysql/)
+- ["Year 2038 problem"](https://en.wikipedia.org/wiki/Year_2038_problem)
+
 ## Related Tasks
 
 https://lab.civicrm.org/dev/core/-/issues/3152