def is_known_field(self, field_name):
        return True
Retrieve diff file from the server.
dataset/ETHPy150Open Kinto/kinto/kinto/views/records.py/Record.is_known_field--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/google/appengine/tools/appcfg.py/IndexOperation.DoDiff