WordPress at a glance
function is not described

stripos() WP 1.0

For php4 compatibility

No Hooks.

Return

Null. Nothing.

Usage

stripos( $haystack, $needle );

Code of stripos() WP 5.5.1

<?php
function stripos($haystack, $needle){
    return strpos($haystack, stristr( $haystack, $needle ));
}