___________________ scalar context pad fetch. autovivifies
  /   ________________ deref
 |   /    ____________ scalar context hash fetch. autovivifies
 |  |    /     _______ deref
 |  |   |     /   ____ void context hash fetch. warns.
 |  |   |    |   /
|--|-|------|-|----|
$hr->{stuff}->{foo};