Per-row validation

I'm not sure if this is already available but something to consider for V6 is a per-row validation callback. What I'd like to do is get the row data, as an object with keys if header: true or indexes if not, and be able to return true if the row is good or an error reason if it's garbage. This allows the errors to be handled in one place (vs detecting errors returned by the parser and then having to iterate, remove bad rows, and handle that errors list separately).

I'm trying to decide if it would be better for this callback to happen before or after transforms. Either way works for my use but maybe that could be configurable.

{
    rowValidation: (rowData) => {
        if (rowData['column1'].trim().length != 10)
            return 'Column 1 incorrect length';

        return true;
    },
    rowValidationPostTransform: true
}