if (my $errs = $errs_tags{$tag}) {
push @violations, do { my $e = pop @$errs; push @$e, $elt; $e };
delete $errs_tags{$tag} unless @$errs;
if (my $errs = $errs_tags{$tag}) {
push @violations, do { my $e = pop @$errs; push @$e, $elt; $e };
delete $errs_tags{$tag} unless @$errs;