[ns]Meaning of $self, $class, $proc

[cwlau@stdhk.com]

Hello

I am a newbie in ns. I am studying the ns document. Could anyone please tell
me the meaning and usage of the following variables ?

1. $self
2. $class
3. $proc

They appear in page 26 of the ns document in argv[1...3].
I cannot find further illustration or explanation in the rest of the 
document. 

I have also searched the archive which tells me to refer to the ns document
but I still cannot find their neaning and usage.


Could anyone please point me to some reference ?

Thank you very much.