Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Calculation/TextData.php
public static function SEARCHINSENSITIVE($needle, $haystack, $offset = 1)
    {
        $needle = Functions::flattenSingleValue($needle);
        $haystack = Functions::flattenSingleValue($haystack);
        $offset = Functions::flattenSingleValue($offset);

        if (!is_bool($needle)) {
            if (is_bool($haystack)) {
                $haystack = ($haystack) ? Calculation::getTRUE() : Calculation::getFALSE();
            }

            if (($offset > 0) && (StringHelper::countCharacters($haystack) > $offset)) {
                if (StringHelper::countCharacters($needle) == 0) {
                    return $offset;
                }

                $pos = mb_stripos($haystack, $needle, --$offset, 'UTF-8');
                if ($pos !== false) {
                    return ++$pos;
                }
            }
        }

        return Functions::VALUE();
    }
public static function SEARCHINSENSITIVE($needle, $haystack, $offset = 1)
    {
        $needle = Functions::flattenSingleValue($needle);
        $haystack = Functions::flattenSingleValue($haystack);
        $offset = Functions::flattenSingleValue($offset);

        if (!is_bool($needle)) {
            if (is_bool($haystack)) {
                $haystack = ($haystack) ? Calculation::getTRUE() : Calculation::getFALSE();
            }

            if (($offset > 0) && (StringHelper::countCharacters($haystack) > $offset)) {
                if (StringHelper::countCharacters($needle) == 0) {
                    return $offset;
                }

                $pos = mb_stripos($haystack, $needle, --$offset, 'UTF-8');
                if ($pos !== false) {
                    return ++$pos;
                }
            }
        }

        return Functions::VALUE();
    }
SEARCHINSENSITIVE.

@param string $needle The string to look for
@param string $haystack The string in which to look
@param int $offset Offset within $haystack

@return string