Upload multiple files

Hi,

I want to do upload multiple files and  I can do this in cycle.

But first I looked source code of Upload library and found the part of the library code. And I can't understand this code. What does this code?

P.S: If my file field in form has name user[photo] and in do_upload() I passing user while file not selected (empty form submitted) that I get a PHP error:

Code:

Severity: Warning
Message: is_uploaded_file() expects parameter 1 to be string, array given
Filename: libraries/Upload.php
Line Number: 412

instead of a CI message about file not selected.

1. How can I upload a few files without a cycle?
   
2. How can I upload a file with field name like user[photo]?
   
3. Why do I have error in the case with empty form? Is it a bug with unhandled error?
   
4. What does the code by link above?
   

Thanks!