my ($label) = @_;
length($label) >= $L_MAX and
return "`$label' too long (must be <= $L_MAX)";
+ $label =~ /[A-Z]/ and
+ return "`$label' must be lowercase";
$label =~ m{\A[a-z0-9_](?:[a-z0-9_\-\./\@,]*[a-z0-9])?\z} ?
undef : "`$label' is invalid";
},