This package provides utility routines for sorting and grouping. Specifically, it contains a QuickSort implementation, and some `AtomicComparer` objects that handle character and numeric comparisons, together with the important `DocumentOrderIterator` which iterates over a set of nodes in document order.

The package also contains the classes to support the implementation of the XSLT 2.0 instruction `xsl:for-each-group`, and some utilities for maintaining sets and maps whose keys are unboxed integer values.