def clean(self):
if not self.staffCategory and not self.staffMember:<EOL><INDENT>raise ValidationError(_('<STR_LIT>'))<EOL><DEDENT>if self.staffCategory and self.staffMember:<EOL><INDENT>raise ValidationError(_('<STR_LIT>'))<EOL><DEDENT>
Either staffCategory or staffMember must be filled in, but not both.