System V and POSIX timezone strings

 An instance of this class represents a timezone that was specified by means
 of a System V timezone string or the POSIX extended form of the same syntax.
 These can express a plain offset from Universal Time, or a system of two
 offsets (standard and daylight saving time) switching on a yearly cycle
 according to certain types of rule.
 .
 DateTime::TimeZone::SystemV implements the DateTime::TimeZone interface, so
 that its instances can be used with DateTime objects.