The Levenshtein distance is a metric for measuring the amount of difference
between two sequences (i.e., the so called edit distance). The Levenshtein
distance between two sequences is given by the minimum number of operations
needed to transform one sequence into the other, where an operation is an
insertion, deletion, or substitution of a single element.

The two sequences can be two strings, two arrays, or two other objects.
Strings, arrays and arrays of strings are handled with optimized (very fast) C
code. All other sequences are handled with generic (fast) C code.

More information about the Levenshtein distance algorithm:
http://en.wikipedia.org/wiki/Levenshtein_distance .