$self->{copybooks} = [
    Cobol::Copybook->new({filehandle => \*DATA, filter => '00'}),
    Cobol::Copybook->new({filehandle => \*DATA, filter => '01'}),
    undef,
    undef,
    Cobol::Copybook->new({filehandle => \*DATA, filter => '04'}),
];