could you just explain what's going on inside the map function please?

Sure.

sub fuzzyMatch {
    my( $rHay, $rNee, $misses ) = @_;
    my $lNee = length $$rNee;
    my $min = $lNee - $misses;

    map {
        (
             ( substr( $$rHay, $_, $lNee ) ^ $$rNee ) =~ tr[\0][] 
        ) >= $min ? $_ : ()
    } 0 .. length( $$rHay ) - $lNee;
}
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• We need to compare the needle against the haystack at each position.

  Hence the map counter runs from 0 to length( haystack) - length( needle ).

• We need to compare the same number of characters from the haystack as there are in the needle.

  Hence, the substr presents a needle length substring of haystack at each of those counter positions.

• We don't just want a yes/no comparison; we need a count of the differences.

  So we bit-wise xor (^) the substring and the needle.

  The result is a string that has a 0 (null) byte wherever the two strings match; and some other byte value where they do not.

• We need to count the zero bytes.

  tr[\0][] does that efficiently.

• If the count of matched bytes is greater than the minimum required (length( needle ) - misses)

  return the position where the match occurred ($_), otherwise return nothing (()).

Hope that clarifies things little. Continue to ask about anything that isn't clear.