A rule on a bridge interface that uses arp or rarp may be followed with a literal "request" or "reply" (cf. sbin/ifconfig/brconfig.c L1041 and 1048), so the Ar macro is incorrect as it's argument is not a placeholder.
Aside: Is there a rule for when to list alternatives with foo | bar or foo Ns | Ns bar? in/out, arp/rarp, and request/reply are all the former sans-Ns; however, block/pass uses the Ns macro. diff --git ifconfig.8 ifconfig.8 index c522491ad45..2d1d2eb1974 100644 --- ifconfig.8 +++ ifconfig.8 @@ -751,7 +751,7 @@ like a hub or a wireless network. .Bk -words .Op Cm tag Ar tagname .Oo -.Cm arp | rarp Op Ar request | reply +.Cm arp | rarp Op Cm request | reply .Op Cm sha Ar lladdr .Op Cm spa Ar ipaddr .Op Cm tha Ar lladdr