Additionally the information in the time zone database shipped with the ICU library may be outdated. Please refer
to the [ICU manual](http://userguide.icu-project.org/datetime/timezone#TOC-Updating-the-Time-Zone-Data) for details
on updating the time zone database. While for output formatting the ICU timezone database is used, the time zone database
used by PHP may be relevant too. You can update it by installing the latest version of the [pecl package `timezonedb`](http://pecl.php.net/package/timezonedb).