nicnt and nki files explanation

I've searched Youtube and Googled and cannot find a clear, simple explanation.

I understand a standalone nki file and can drag it into Kontakt and play the instrument. So far so good.

But could somebody explain to this newbie the nicnt file clearly and simply ?

What does it have in it ? nki's ? samples ? instruments, registry info, images ?

And why ?

And what is an nicnt file used for beyond the nki file and how do you use it ? Can you drag it into Kontakt and something will play ?

And if I can open an instrument with an nki file what do I need an nicnt file for ?

Do some libraries/instruments only have and need nki files and others need the nicnt ?

I'm sure this has been asked before so if somebody just has a pointer or link to an explanation I would really appreciate it.

Best,

Bob