Make the second, section number argument of .Xr mandatory.

In fact, we have been requiring it for many years.
The only reason to not warn when it was missing
was excessive traditionalism - it was optional in 4.4BSD.

1 files changed, 7 insertions, 0 deletions

diff --git a/mandoc.1 b/mandoc.1
index c8ed310f..65616272 100644
--- a/mandoc.1
+++ b/mandoc.1
@@ -1147,6 +1147,13 @@ macro is immediately followed by an
 .Ic \&Re
 macro on the next input line.
 Such an empty block does not produce any output.
+.It Sy "missing section argument"
+.Pq mdoc
+An
+.Ic \&Xr
+macro lacks its second, section number argument.
+The first argument, i.e. the name, is printed, but without subsequent
+parantheses.
 .It Sy "missing -std argument, adding it"
 .Pq mdoc
 An