This seems quite clear to me, though perhaps a bit abstract. My primary suggestion would be to include some kind of basic example data structure ('Fruit' -> 'Apple' -> 'Granny Smith') with a few notions of how someone might use your module to build an application. I think I understand what the module is for, but I cannot quite see how or for what I would be able to use it.

I thought that the spreadsheet comparison is a bit too simple because it does not involve any kind of tree structure (afaics, but maybe I'm just not a spreadsheet expert). Your target audience obviously will be savy enough to understand the distinction between rulesets and data.

But overall, the writing seems quite clear to me.

sub sk{ return unless $in = shift;
        $in =~ s!(.)$!!; print $1; sk($in)}
sk("gro.alubaf@yehaf");
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