$VAR1 = {
    'Stuff1' => 'Data Stuff',
    'ImportantStuff' => {
      'MoreStuff' => {
         ...
      },
      'VeryImportantStuff' => {
         'Item1' => {
            'Description' => 'Need To Know',
            'Date' => '20040101',
         },
         'Item2' => {
            ...
         },
         'Item3' => {
            ...
         },
      },
   },
};

##</code><code>##

#pseudo code
struct SubFields => {
   Description => '$',
   Date => '$',
};

my $s = XML::Simple->new;
my $tree = $s->XMLin($someFile);
my $subfields = SubFields->new();

$subfields->Description ( $tree->{ImportantStuff}->{VeryImportantStuff}->{Item1}->{Description} );

print Dumper($subfields);
print Dumper($tree);


##</code><code>##

$VAR1 = bless({
   'SubFields::Description' => undef,
   'SubFields::Date' => undef,
}, 'SubFields');

$VAR1 = {
    'ImportantStuff' => {
      'VeryImportantStuff' => {
         'Item1' => {}
         }
      },
    },
    'Stuff1' => 'Data Stuff',
    'ImportantStuff' => {
      'MoreStuff' => {
         ...
      },
      'VeryImportantStuff' => {
         'Item1' => {
            'Description' => 'Need To Know',
            'Date' => '20040101',
         },
         'Item2' => {
            ...
         },
         'Item3' => {
            ...
         },
      },
   },
};