When the standard comparison operators are not applicable to your task, you may specify your own search algorithm using the Btree.Extract user index facility. The Btree.Extract user index facility consists of two parts: a parsing module and a compare module. The parsing module is a pre-process to Btree.Extract that determines whether the search value should cause Btree.Extract to call a custom comparison module. The compare module is called as an alternative to the comparison logic usually done by Btree.Extract.