+sub default_from_access_cfg ($$$;$) {
+ my ($var, $keybase, $defval, $permit_re) = @_;
+ return if defined $$var;
+
+ $$var = access_cfg("$keybase-newer", 'RETURN-UNDEF');
+ $$var = undef if $$var && $$var !~ m/^$permit_re$/;
+
+ $$var //= access_cfg($keybase, 'RETURN-UNDEF');
+ $$var //= $defval;
+
+ badcfg f_ "unknown %s \`%s'", $keybase, $$var
+ if defined $permit_re and $$var !~ m/$permit_re/;
+}
+