This part of the documentation is very important:

For the moment, the specifics of this class are remaining undocumentated.
Please read the code for more information, API is subject to change.

Because this is the code for the add method

sub add {
    my $self = shift;
    my $path = shift;
    unless ( defined _STRING($path) ) {
        croak("Did not provide a path to ->add");
    }
    die "CODE INCOMPLETE";
}
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The save method looks like it probably works. You can get the path add, add it on yourself, and then save() the result.