I would use can for this. That way, whether your filters inherit functions from parents or import them, your query will work correctly.

    sub My::Filters::known { }
    sub My::Filters::forward;
    for my $string (qw[known unknown forward]) {
        warn $string if My::Filters->can($string);
    }
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As a bonus, you can define the package with a variable with can:

    sub My::Filters::known { }
    sub My::Filters::forward;
    sub My::Other::Filters::forward;
    for my $package (qw[My::Filters My::Other::Filters]) {
        for my $func (qw[known unknown forward]) {
            warn $package . '::' . $func if $package->can($func);
        }
    }
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