.Xo/.Xc outside an .It header or a block-partial-implicit macro body seems to
be a no-op on present mandoc and is not a documented use-case. ascii and
html output are identical before and after.

If I'm wrong about the above in some way I will appreciate correction,
as I am working on an mdoc(7) parser in another setting, and naturally
mandoc(1) is my reference implementation and the OpenBSD manuals are my
reference corpus.

E

diff /usr/src
commit - 208893442c38e0767db1293632337acc2532616c
path + /usr/src
blob - d60769e2763926cb4fc4d431eea79e0bd0d5da94
file + bin/ksh/ksh.1
--- bin/ksh/ksh.1
+++ bin/ksh/ksh.1
@@ -1800,10 +1800,8 @@ command may be used to list, change, and add to this c
 Brace expressions take the following form:
 .Bd -unfilled -offset indent
 .Sm off
-.Xo
 .Ar prefix No { Ar str1 No ,...,
 .Ar strN No } Ar suffix
-.Xc
 .Sm on
 .Ed
 .Pp
blob - 86145e812e7e26fc4e324a5733d0e376704d9b2e
file + usr.bin/dig/dig.1
--- usr.bin/dig/dig.1
+++ usr.bin/dig/dig.1
@@ -307,11 +307,9 @@ The query options are:
 .Cm aaflag
 .Xc
 A synonym for
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm aaonly .
-.Xc
 .It Xo
 .Cm + Ns
 .Op Cm no Ns
@@ -413,11 +411,9 @@ is automatically set when
 is in use, to better emulate the default queries from a name server.
 .Pp
 This option was formerly called
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm sit
-.Xc
 (Server Identity Token).
 In BIND 9.10.0 through BIND 9.10.2,
 it sent the experimental option code 65001.
@@ -425,17 +421,13 @@ This was changed to option code 10 in BIND 9.10.3 when
 COOKIE option was allocated.
 .Pp
 The
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm sit
-.Xc
 option is now deprecated, but has been retained as a synonym for
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm cookie
-.Xc
 for backward compatibility within the BIND 9.10 branch.
 .It Xo
 .Cm + Ns
@@ -453,7 +445,6 @@ the key id is displayed as the replacement, e.g. "[ ke
 .Cm defname
 .Xc
 Deprecated, treated as a synonym for
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm search
@@ -462,7 +453,6 @@ Deprecated, treated as a synonym for
 .Cm + Ns
 .Op Cm no Ns
 .Cm dnssec
-.Xc
 Request DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT
 record in the additional section of the query (off by default).
 .It Cm +domain Ns = Ns Ar name
@@ -650,7 +640,6 @@ is returned (on by default).
 .Cm rdflag
 .Xc
 A synonym for
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm recurse
@@ -659,7 +648,6 @@ A synonym for
 .Cm + Ns
 .Op Cm no Ns
 .Cm recurse
-.Xc
 Set the RD (recursion desired) bit in the query (on by default).
 Recursion is automatically disabled when the
 .Cm +nssearch
@@ -817,11 +805,9 @@ Display the TTL when printing the record (on by defaul
 .Xc
 Use TCP when querying name servers.
 This alternate syntax to
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm tcp
-.Xc
 is provided for backwards compatibility.
 The "vc" stands for "virtual circuit".
 .El
@@ -848,11 +834,9 @@ also be supplied.
 These global query options must precede the first tuple of name, class, type,
 options, flags, and query options supplied on the command line.
 Any global query options (except the
-.Xo
 .Cm + Ns
 .Op Cm no Ns
 .Cm cmd
-.Xc
 option) can be overridden by a query-specific set of query options.
 For example:
 .Bd -literal -offset indent
blob - f3fef23abb446ef5d840bfe20fb24d29db14a566
file + usr.bin/ssh/ssh_config.5
--- usr.bin/ssh/ssh_config.5
+++ usr.bin/ssh/ssh_config.5
@@ -1585,14 +1585,12 @@ ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 
 .Ed
 .It Cm ProxyJump
 Specifies one or more jump proxies as either
-.Xo
 .Sm off
 .Op Ar user No @
 .Ar host
 .Op : Ns Ar port
 .Sm on
-or an ssh URI
-.Xc .
+or an ssh URI.
 Multiple proxies may be separated by comma characters and will be visited
 sequentially.
 Setting this option will cause
blob - 2b382bf50de01a76991cb559c4d8fa966ad91285
file + usr.bin/systat/systat.1
--- usr.bin/systat/systat.1
+++ usr.bin/systat/systat.1
@@ -265,10 +265,8 @@ The
 .Dq State
 column has the format
 .Sm off
-.Xo
 .Cm up | dn
 .Bq : Cm U | D .
-.Xc
 .Sm on
 .Sq up
 and