sub store_position
 {
 my( $t, $elt)= @_;
 my $line   = $t->{twig_parser}->current_line;    # $t->{twig_parser} is the expat object
 my $column = $t->{twig_parser}->current_column;
 $elt->{custom_atts}{position}= [$line, $column];   # crude but works
 }