[... clock ...]
"The current set of places where it will try to find Olson files is:
/usr/share/zoneinfo /user/share/lib/zoneinfo /user/lib/zoneinfo /user/local/etc/zoneinfo C:/Progra~1/cygwin/usr/local/etc/zoneinfo
That's what's done if a search for a Tcl time zone definition in $tcl_library/tzdata fails.
In addition, the set of hardcoded time zone names in ::tcl::clock::LegacyTimeZone is recognized, as is any Posix time zone specifier, and the special name 'localtime'."