diff --git a/lib/libc/net/resolver.3 b/lib/libc/net/resolver.3
--- a/lib/libc/net/resolver.3
+++ b/lib/libc/net/resolver.3
@@ -34,6 +34,7 @@
 .Nm res_mkquery ,
 .Nm res_send ,
 .Nm res_init ,
+.Nm res_findzonecut2 ,
 .Nm dn_comp ,
 .Nm dn_expand ,
 .Nm dn_skipname ,
@@ -84,6 +85,17 @@
 .Ft int
 .Fn res_init void
 .Ft int
+.Fo res_findzonecut2
+.Fa "res_state statp"
+.Fa "const char *dname"
+.Fa "ns_class class"
+.Fa "int options"
+.Fa "char *zname"
+.Fa "size_t zsize"
+.Fa "union res_sockaddr_union *ns"
+.Fa "int nns"
+.Fc
+.Ft int
 .Fo dn_comp
 .Fa "const char *exp_dn"
 .Fa "u_char *comp_dn"
@@ -140,24 +152,15 @@
 should continue until it finds an authoritative answer or finds an error.
 Currently this is not implemented.
 .It Dv RES_USEVC
-Use
-.Tn TCP
-connections for queries instead of
-.Tn UDP
-datagrams.
+Use TCP connections for queries instead of UDP datagrams.
 .It Dv RES_STAYOPEN
 Used with
 .Dv RES_USEVC
-to keep the
-.Tn TCP
-connection open between
-queries.
+to keep the TCP connection open between queries.
 This is useful only in programs that regularly do many queries.
-.Tn UDP
-should be the normal mode used.
+UDP should be the normal mode used.
 .It Dv RES_IGNTC
-Unused currently (ignore truncation errors, i.e., do not retry with
-.Tn TCP ) .
+Unused currently (ignore truncation errors, i.e., do not retry with TCP).
 .It Dv RES_RECURSE
 Set the recursion-desired bit in queries.
 This is the default.
@@ -304,6 +307,49 @@
 \-1 if there were errors.
 .Pp
 The
+.Fn res_findzonecut2
+function locates the nearest enclosing zone cut for domain name
+.Fa dname
+and returns the zone name where delegation occurs
+and the list of name server addresses.
+The
+.Fn res_findzonecut2
+returns 0 on success or -1 on failure.
+.Pp
+The three options supported by
+.Fn res_findzonecut2
+are
+.Bl -tag -width "RES_EXHAUSTIVE"
+.It Dv RES_EXHAUSTIVE
+Always do all queries.
+.It Dv RES_IPV4ONLY
+Only search using IPv4.
+.It Dv RES_IPV6ONLY
+Only search using IPv6.
+.El
+.Bl -column "union res_sockaddr_union *ns" "Description"
+.It Em "Function parameter" Ta Em "Description"
+.It Fa res_state statp Ta Pointer to the resolver state.
+.It Fa "const char *dname" Ta Domain name to inspect,
+e.g. "www.sub.example.com".
+.It Fa "ns_class class" Ta DNS class.
+.It Fa "int options" Ta Options for searching.
+.It Fa "char *zname" Ta Output buffer to hold the zone name at the zone cut,
+e.g. "example.com".
+Note: you must ensure
+.Fa zname
+is large enough to hold a full domain.
+.Dv NS_MAXDNAME
+is often used for buffer size.
+.It Fa "size_t zsize" Ta Size of zname buffer.
+.It Fa "union res_sockaddr_union *ns" Ta Output array of name
+server addresses (IPv4 or IPv6), one per NS.
+.It Fa "int nns" Ta Number of elements available in
+.Fa ns
+array.
+.El
+.Pp
+The
 .Fn dn_comp
 function
 compresses the domain name