(PHP 5 >= 5.2.0, PHP 7)
mb_strripos — Finds position of last occurrence of a string within another, case insensitive
mb_strripos ( string $haystack , string $needle [, int $offset = 0 [, string|null $encoding = null ]] ) : int|false
 mb_strripos() performs multi-byte safe strripos() operation based on number of characters. needle position is counted from the beginning of haystack. First character's position is 0. Second character position is 1. Unlike mb_strrpos(), mb_strripos() is case-insensitive. 
haystack
 The string from which to get the position of the last occurrence of needle 
needle
 The string to find in haystack 
offset
 The position in haystack to start searching 
encoding
Character encoding name to use. If it is omitted, internal character encoding is used.
 Return the numeric position of the last occurrence of needle in the haystack string, or false if needle is not found. 
| Version | Description | 
|---|---|
| 8.0.0 |  encoding is nullable now.  |  
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    https://www.php.net/manual/en/function.mb-strripos.php