In practice the leap seconds tend to be inserted at times of the year that aren't typical DST change season (end of june or end of december) http://en.wikipedia.org/wiki/Leap_second#Insertion_of_leap_seconds

So odds are that in practice it's not a problem. It could be if a jurisdiction decide to change it's timezone at the beginning of the year though.

On 11/09/2013 11:58 AM, Ian Abbott wrote:
On 2013-09-11 16:51, Clive D.W. Feather wrote:
random832@fastmail.us said:
Two things: Can a transition time ever reasonably fall _on_ a leap
second, and can the zic input format represent this case?

It's very unlikely, but theoretically possible.

A leap second would be inserted at 23:59:60 UTC, so I'm not sure it's possible to have a DST transition at the start of a leap second, but you could get a DST transition at the end of a leap second.



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