On the documentation page:
https://doc.ez.no/display/EZP/Search+Criterions+and+Sort+Clauses

Point 1: it is clearly referenced this doc page is intended for both Criterion and Sort Clauses. However, while trying to implement a custom Sort Clause, there is no example to follow on the documentation page, whereas there are a few for Criterion.

Point 2: I believe that at the section "How to configure your own Criterion and Sort Clause Handlers" it should be referenced where (i.e., in which file(s)) the configuration / registration of the Handlers must be inserted.