In the example you have provided,
RecordsetStructure: Attachment
Attachment.fieldSeparator : ,
Attachment.endSeparator: 'nl'
As there is only one field, the fieldseparator will not have any effect on the runtime
I am not sure if having endSeparator as nl will have a effect when you try to open the file or not. You can also leave this as blank.
Regards
Bhavesh