The DateAndTime class supports the standard for time zones which allows DateAndTime calculations and transformations to be more accurate by taking into account time zone information such as Daylight Saving Time (DST) transitions and global time zones.

Implementation of the standard has a Smalltalk code component and a non-Smalltalk data component. From a user perspective, the pertinent code is in the DateAndTime class. The DateAndTime class depends on a time zone database for its calculations.