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    package Filter::Handle;
    use strict;
...
    }

    1;

    my $f = Filter::Handle->new(\*STDOUT,
        sub { "Foo: @_\n" });
    print "Bar";

    use Filter::Handle qw/subs/;
    Filter \*STDOUT, sub { "Foo: @_\n" };
    print "Bar";
    UnFilter \*STDOUT;