docs: def validate_filter(self, key, filter_value):
          """
          validate the filter key and value against the collection schema
          
          :param key: property name
          :param filter_value: value of the filter
          :returns True if all is ok otherwise False
          """
          ok = False
          seek = u"filter[%s]" % key
          value = None
          for link in self.schema['links']:
              if link['rel'] == 'instances':
                 for property in link['properties']:
                     if seek == property:
                         value = link['properties'][property]
                         ok = True
          if not ok:
              return False
          ok = self._is_type(filter_value, value['type'])
          # if string with type add validation
          if ok is True and value['type'] == 'string' and 'format' in value.keys():
              ok = self._validate_json_format(filter_value, value)
              
          return ok