sub output
{
    my $self = shift;

    # mod_perl 2.x
    if ( $ENV{MOD_PERL} )
    {
        eval {
            require Apache::IO;
            Apache::IO->import;
        }; if ($@) {
            die "Cannot figure out what to do under Apache!\n";
        }

        tie *XLS, 'Apache::IO';
        binmode *XLS;
        return $self->write_file(\*XLS);
    }
    # mod_perl 1.x (or CGI under mod_perl 2.x)
    elsif ( $ENV{GATEWAY_INTERFACE} )
    {
        my $module_name;
        eval {
           require Apache;
           Apache->import;
           $module_name = 'Apache';
        }; if ($@) {
            die "Cannot figure out what to do under Apache!\n";
        }

        tie *XLS, $module_name;
        binmode *XLS;
        return $self->write_file(\*XLS);
    }
    # CGI (or non-WWW) behavior
    else
    {
        $self->write_file('-');
    }
}