my %h1 = ( k1 => "v1"  );
my %h2 = ( k2 => \%h1  );
my %h3 = ( k3 => \%h2  );

         %h3
+--------------------+
|       +----------+ |
| k3 => | Ref ------------+
|       +----------+ |    |
+--------------------+    |
                          |
                          v
                         %h2
                +--------------------+
                |       +----------+ |
                | k2 => | Ref -----------+
                |       +----------+ |   |
                +--------------------+   |
                                         |
                                         v
                                        %h1
                               +--------------------+
                               |       +----------+ |
                               | k1 => | Str "v1" | |
                               |       +----------+ |
                               +--------------------+