Checking the file size of an (input type="file")

[cesark]

Does anyone know how this feature works internally in PHP?: (more or less)

"A hidden field (measured in bytes) that precede the file input field, and its value is the maximum filesize accepted. This is an advisory to the browser, PHP also checks it. This form element should always be used as it saves users the trouble of waiting for a big file being transferred only to find that it was too big and the transfer failed."

The complete article is here:

http://us2.php.net/manual/en/features.file-upload.php

I only want to adapt this feature (the advisory to the browser) to my ASP.NET pages.

Thank you