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}");
----
