code: def _validate_keyschema(self, schema, field, value):
          
          if isinstance(value, Mapping):
              validator = self._get_child_validator(
                  document_crumb=field,
                  schema_crumb=(field, 'keyschema'),
                  schema=dict(((k, schema) for k in value.keys())))
              if not validator(dict(((k, k) for k in value.keys())),
                               normalize=False):
                  self._drop_nodes_from_errorpaths(validator._errors,
                                                   [], [2, 4])
                  self._error(field, errors.KEYSCHEMA, validator._errors)
docs: {'type': ['dict', 'string'], 'validator': 'bulk_schema',
              'forbidden': ['rename', 'rename_handler']}