In a released products external item description (either under purchase tab or sales tab), you can add external item descriptions for a specific vendor / customer in "Vendor / Customer relation". However, when you change the "Account code" to "group", instead of choosing Vendor groups or Customer groups, "Vendor / Customer relation" now chooses "external item description group",which does not seems to be related to group of customers or vendors.
So, my question is what is the usage of this "external item description group", and how do it make my external item descriptions apply for a group of vendors or customers?