To make it nice and portable, consider using File::Spec (or its functional sibling File::Spec::Functions. Using that, you don't have to have the DIR_SEP variable, as you can use catdir. For example:

my $pathname = $self->{'root'} . $DIR_SEP . $leaf;
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becomes

my $pathname = catdir($self->{'root'}, $leaf);
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Also

return -e ($self-{'root'} .  $DIR_SEP . $leaf);
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will probably not do what you expect. New testcase ;-)

Arjen