relationship with module Documents: ForContractType

When I create a relationship (many to many) in Studio with the module Documents, I can choose in “Subpanel for Documents” either “default” or “ForContractType”.

What effect does choosing “ForContractType” have on the relatinship/suppanel’s behavior? I couldn’t tell any difference.

thanks!

Also: What’s the meaning of the field “Contract name” in module Documents? It doesn’t show up in the list of module fields, but it shows up in the Layout-Builder. Seems to be a Text-field.