ql:has-relation not documented

[SimonSelg]

There is only one example query:

PREFIX we: <http://www.wikidata.org/entity/>
PREFIX wp: <http://www.wikidata.org/prop/direct/>
SELECT ?r (COUNT(?r) as ?count) WHERE {
  ?a wp:P106 we:Q11631 .
  ?a ql:has-relation ?r
}
GROUP BY ?r
ORDER BY DESC(?count)

Could ql:has-relation please be documented?