What values do I fill in the UserID box when creating a user template? (4269091)

What values do I fill in the UserID box when creating a user template?

Any templates that are used by Active Directory or Generic Integration and have a WinAD primary Authentication type, the Primary User ID must be empty or one of the following values (not case-sensitive): UPN, UserPrimaryName, SAMAccountName.
If any external authentication is set the ExternalUserID must still be populated to save the template, however when a user is created from the template the UserName will be used as the default ExternalID.