====== PHP RFC: Add locale for case insensitive grapheme functions ======
  * Version: 2.0
  * Date: 2025-06-07 
  * Author: Yuya Hamada, youkidearitai@gmail.com
  * Status: Under Discussion
  * First Published at: https://wiki.php.net/rfc/grapheme_add_locale_for_case_insensitive

===== Introduction =====
A grapheme functions is not locale dependency. This RFC is add locale parameter for grapheme case insensitive functions. That is more enhancements for Unicode can be expected.

  * grapheme_strpos
  * grapheme_stripos
  * grapheme_strrpos
  * grapheme_strripos
  * grapheme_strstr
  * grapheme_stristr
  * grapheme_levenshtein

By this RFC can cover locale. For example.

<code>
var_dump(grapheme_stripos("i", "\u{0130}", 0, "tr_TR")); // Result is 0
var_dump(grapheme_stripos("i", "\u{0130}", 0, "en_US")); // Result is false
</code>



===== Proposal =====

Add a $locale parameter and $strength parameter in these functions.

<code>
function grapheme_strpos(string $haystack, string $needle, int $offset = 0, string $locale = ""): int|false {}
function grapheme_stripos(string $haystack, string $needle, int $offset = 0, string $locale = ""): int|false {}
function grapheme_strrpos(string $haystack, string $needle, int $offset = 0, string $locale = ""): int|false {}
function grapheme_strripos(string $haystack, string $needle, int $offset = 0, string $locale = ""): int|false {}
function grapheme_substr(string $string, int $offset, ?int $length = null, string $locale = ""): string|false {}
function grapheme_strstr(string $haystack, string $needle, bool $beforeNeedle = false, string $locale = ""): string|false {}
function grapheme_stristr(string $haystack, string $needle, bool $beforeNeedle = false, string $locale = ""): string|false {}
function grapheme_levenshtein(string $string1, string $string2, int $insertion_cost = 1, int $replacement_cost = 1, int $deletion_cost = 1, string $locale = ""): int|false {}
</code>

Specifying strength can change the match for CJK characters, For example:

<code>
$nabe = '邊';
$nabe_E0101 = "邊\u{E0101}";
var_dump(grapheme_levenshtein($nabe, $nabe_E0101)); // result is 0
var_dump(grapheme_levenshtein($nabe, $nabe_E0101, locale: "ja_JP-u-ks-identic")); // result is 1
var_dump(grapheme_strpos($nabe, $nabe_E0101)); // result is 0
var_dump(grapheme_strpos($nabe, $nabe_E0101, locale: "ja_JP-u-ks-identic")); // result is false
</code>

If $locale is not valid, returns false and set ''intl_error_code_set'' and ''intl_error_set_custom_msg''. Therefore, PHP userland can use ''intl_get_error_code'' and ''intl_get_error_message'' for reason.

grapheme_stri* The strength of the function remains unchanged and UCOL_SECONDARY is used.

The reason for removing $strength is to avoid complexity and because it can be specified with $locale.

===== Backward Incompatible Changes =====
Nothing if added parameter is default values.

===== Proposed PHP Version(s) =====
8.5

===== RFC Impact =====
==== To SAPIs ====
No effects.

==== To Existing Extensions ====
No effects.

==== To Opcache ====
No effects.

==== New Constants ====
No effects.

===== Open Issues =====
Nothing.

===== Future Scope =====
This section details areas where the feature might be improved in future, but that are not currently proposed in this RFC.

===== Proposed Voting Choices =====

I am sorry for stopping vote. I'll fix this RFC.

===== Patches and Tests =====
https://github.com/php/php-src/pull/18792

===== Implementation =====
https://github.com/php/php-src/pull/18792

===== References =====
https://unicode-org.github.io/icu/userguide/transforms/casemappings.html#full-language-specific-case-mapping

===== Rejected Features =====
Keep this updated with features that were discussed on the mail lists.