adding models

Hey guys,

Wondering about how to add models in Gnucap I read part 6 of this 
manual :
http://www.gnu.org/software/gnucap/gnucap-man.pdf

Could you explain what the enhanced subcircuit corresponds to or give 
some references I could check ?

In the end, I must say I am really interested in the "Primitive" way to 
add them.

Since the manual doesn't talk about that, I was wondering if you had a 
draft manual introducing to working with "primitive", or maybe a "hello 
world" example and maybe a slightly more complicated example.

As always, Thanks for reading.
Romain.