I am planning to add xl2csv as another filter to parse MS Excel files besides the XLtoHTML.pm filter.  I copied Doc2txt.pm and made it xls2csv.pm with the following changes:

package SWISH::Filters::xls2csv;
use vars qw/ %FilterInfo $VERSION /;


$VERSION = '0.01';

%FilterInfo = (
    type     => 2,  # normal filter
    priority => 50, # normal priority 1-100
);

sub filter {
    my $filter = shift;

    # Do we care about this document?
    return unless $filter->content_type =~ m!application/vnd.ms-excel!;

    # We need a file name to pass to the xls2csv program
    my $file = $filter->fetch_filename;

    # Grab output from running program
    my $content = $filter->run_program( 'xls2csv', $file );

    # update the document's content type
    $filter->set_content_type( 'text/plain' );

How and where do I specify that xls files should be parsed by both filters.  And how do I specify that the output of xls2csv should be parsed by the TXT2 parser?

Thank you for your help.