package Foo;

use Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw(access_internal_var);

use strict;

my %Internal_Var_Here;

sub access_internal_var {
    # Insert code here to access the hash
}
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Now, in Perl5.6, you get the our keyword. That would modify the above as such:

use strict;

package Foo;

use Exporter;
our @ISA = qw(Exporter);
our @EXPORT_OK = qw(access_internal_var);
.
.
.
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The reason I say that this is sane design is that this acts as encapsulation of global variables in a very local way.