Additional Fields in Bulk Send

Hi,

I understand additional fields can be put in the CSV for bulk send to populate custom data into a transaction by adding extra columns that map to fields in the template. Is there a limitation on the number of fields for each row in the CSV?

If there is a limitation is it per signer or is it for the whole row? I.e. if multiple signers and a limited amount of fields allowed is that split between signers since all on the one row for one transaction.