code: function check(
    source: RecordSource,
    target: MutableRecordSource,
    selector: NormalizationSelector,
    handlers: $ReadOnlyArray<MissingFieldHandler>,
    operationLoader: ?OperationLoader,
    getDataID: GetDataID,
  ): boolean {
    const {dataID, node, variables} = selector;
    const checker = new DataChecker(
      source,
      target,
      variables,
      handlers,
      operationLoader,
      getDataID,
    );
    return checker.check(node, dataID);
  }
docs: Synchronously check whether the records required to fulfill the given
  `selector` are present in `source`.
  
  If a field is missing, it uses the provided handlers to attempt to substitute
  data. The `target` will store all records that are modified because of a
  successful substitution.
  
  If all records are present, returns `true`, otherwise `false`.