Assignment to array element reference does not count as a write

[sirbrillig]

static function dotToMultiArray(
    array $array
): array {
    $multi = [];
    foreach($array as $key => $value){
        $level = &$multi;
        foreach(explode(".", $key) as $node)
            $level = &$level[$node];
        $level = $value;
    }
    return $multi;
}

This marks $level as unused but the third assignment actually changes the referenced variable.