Ambiguous DATE-TIME values when clocks go back

[Damon Chaplin <damon@xxxxxxxxxx>]

I've just noticed there is no way to differentiate between the duplicated
times when clocks go back.

When clocks go back, say from 2am to 1am, you get the same hour
twice. So having a DTSTART like this is ambiguous:

   DTSTART;TZID=Europe/London:20011028T013000

It could be 1:30am local standard time or 1:30am daylight saving time.

(And similarly for any timezone change where the time is shifted back.)

Damon