Question about :sub-program

I have a minor question about assembler syntax. What's the
:sub-program frobnitz supposed to be doing here?

   (:jnz '(:sub-program () (:int 66)))

Sometimes I see it with an argument:

   (:jl '(:sub-program (failed)
          (:int 112)
          (:halt)
          (:jmp 'failed)))

It seems like it's an embedded subroutine. Am I right? I'm having a
hard time working out its semantics from the reader.

'james

-- 
James A. Crippen <james at unlambda.com> Lambda Unlimited
61.2204N, 149.8964W                      Recursion 'R' Us
Anchorage, Alaska, USA, Earth            Y = \f.(\x.f(xx))(\x.f(xx))