package A;

use strict;
use Exporter qw(import);
our @EXPORT = qw($maxlengths);

our $maxlengths = {
    tinytext => 100,
    text => 200,
    mediumtext => 500,
    longtext => 2000
};

# and several others like this

1;

package B;

use strict;
use A qw($maxlengths);

# contrived
sub check_form {
    my $self = shift;
    if (length($self->{address}) > $maxlengths->{tinytext}) {
        # code to trigger error
    }
}

1;