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Clarify regex character range case insensitivity limitations #125413

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Mar 21, 2025
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Clarify regex character range case insensitivity limitations #125413

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Update regexp-syntax.md
leemthompo Mar 21, 2025
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use md syntax
leemthompo Mar 21, 2025
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7 changes: 7 additions & 0 deletions docs/reference/query-languages/query-dsl/regexp-syntax.md
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Expand Up @@ -138,6 +138,13 @@ A `^` before a character in the brackets negates the character or range. For exa
[^abc\-] # matches any character except 'a', 'b', 'c', or '-'
```

:::{note}
Character range classes such as `[a-c]` do not behave as expected when using `case_insensitive: true` — they remain case sensitive. For example, `[a-c]+` with `case_insensitive: true` will match strings containing only the characters 'a', 'b', and 'c', but not 'A', 'B', or 'C'. Use `[a-zA-Z]` to match both uppercase and lowercase characters.

This is due to a known limitation in Lucene's regular expression engine.
See [Lucene issue #14378](https://github.com/apache/lucene/issues/14378) for details.
:::


## Optional operators [regexp-optional-operators]

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