## Why is this an issue?

When using POSIX classes like `\p{Alpha}` without the `UNICODE_CHARACTER_CLASS` flag or when using hard-coded character classes like `"[a-zA-Z]"`, letters outside of the ASCII range, such as umlauts, accented letters or letter from non-Latin languages, won’t be matched. This may cause code to incorrectly handle input containing such letters.

To correctly handle non-ASCII input, it is recommended to use Unicode classes like `\p{IsAlphabetic}`. When using POSIX classes, Unicode support should be enabled by either passing `Pattern.UNICODE_CHARACTER_CLASS` as a flag to `Pattern.compile` or by using `(?U)` inside the regex.

### Noncompliant code example

    Pattern.compile("[a-zA-Z]");
    Pattern.compile("\\p{Alpha}");

### Compliant solution

    Pattern.compile("\\p{IsAlphabetic}"); // matches all letters from all languages
    Pattern.compile("\\p{IsLatin}"); // matches latin letters, including umlauts and other non-ASCII variations
    Pattern.compile("\\p{Alpha}", Pattern.UNICODE_CHARACTER_CLASS);
    Pattern.compile("(?U)\\p{Alpha}");