Errors encountered in describing limitation parameter in documentation for calls creating a policy:
https://github.com/ezsystems/ezpublish-
kernel/blob/master/doc/specifications/rest/REST-API-V2.rst#create-policy
or updating one:
https://github.com/ezsystems/ezpublish-kernel/blob/master/doc/specifications/rest/REST-API-V2.rst#update-policy

The limitatation format which is actually working is as follows (JSON format):

{  _identifier : "Class",
        values : {
           ref : [{
                _href : "18"
            }]
        }
}

while documentation states _href should be full resource id.
E.g.

_href : "/api/ezp/v2/content/types/18"

Also, for "create Policy" call Resource, Method and Description are mistakenly taken from "Update Policy" section