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docs: document Unicode behavior for Levenshtein #70

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Expand Up @@ -124,6 +124,27 @@ public class MyApp {
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### Unicode representation

This implementation operates on Java `String` values using `String.length()`
and `charAt()`. These APIs expose UTF-16 code units rather than Unicode code
points or user-perceived characters.

As a result, a supplementary Unicode code point represented by a surrogate pair
can occupy two sequence positions in the Levenshtein calculation.

This distinction does not change the Levenshtein recurrence itself; it defines
the sequence elements supplied to the algorithm. Code-unit distance can
therefore differ from Unicode code-point or grapheme-cluster distance for some
text.

Applications that require code-point or grapheme-cluster semantics should
convert or segment the input into the intended sequence units before computing
the distance.

For additional background on runtime string representations and edit-distance
implementations, see [Levenshtein implementations and Unicode sequence units](https://www.levenshtein.net/levenshtein-implementations).

## Normalized Levenshtein
This distance is computed as levenshtein distance divided by the length of the longest string. The resulting value is always in the interval [0.0 1.0] but it is not a metric anymore!

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