The Sort Criteria objects extend the standard SortCollection with an easy to use, simple yet powerful and dynamic sorting capability that can sort multiple 'columns' or 'attributes' of a collection of objects. It's easy to rearrange the column sort ordering and the acending or decending state of the sort. It's simple because it just works with SortedCollections as you currently use them. It's powerful because you can sort any sequence of attributes in an object. It's dynamic as a SortCriteria and it's columns can be created on the fly by a user interface enabling the user to choose their own sort order and ascending/decending sequence.
The SortCriteria and SortCriteriaColumn (and SortCriteriaTest for an example) are the classes that are added to the Smalltalk system. No changes to SortedCollection were required or other Smalltalk system classes.