code: private static String errorReasonFor( URL location, List<String> errors)
      {
      return
        Stream.concat(
          Stream.of( String.format( "%s conformance problem(s) found in Open API document%s", errors.size(), locationId( location))),
          IntStream.range( 0, errors.size()).mapToObj( i -> String.format( "[%s] %s", i, errors.get(i))))
        .collect( joining( "\n"));
      }
docs: Returns a reason for the errors in the document at the given location.