WordPress at a glance
function is not described

stripos() WP 1.0

No Hooks.

Return

Nothing (null).

Usage

stripos( $haystack, $needle );

Code of stripos: wp-includes/class-pop3.php VER 5.0.3

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