Thank you - I'd found that, but it doesn't explain how to do exactly the part I need, which is how to add a new multiline tab to an existing form, and for that multiline tab to enable me to create new records in a new model that will be linked to the model of the original form. So, the customer form already exists, but a list of relationships a customer has with other customers doesn't. So I need to create a new model "relationships", which then has to be related to the original customer model (customer code or name being the linking field). And when I create new lines, each one automatically is populated with the customer number/name that I am currently editing and I just fill in the info on the other fields.