In part I, I described the linear programming bound for additive codes. It turns out that this bound can be extended to general codes, as I will be describing in part II. As the fundamental objects in the additive LP bound are the weight enumerators associated to a code, so in the general case, we need analogues of weight enumerators for general codes. This role is played, as we will see, by the Shor-Laflamme enumerators and the quantum shadow enumerator. With this, we get a bound for general codes very nearly as strong as the bounds for additive codes.
Additional references for part II:
"Quantum analog of the MacWilliams identities in classical coding theory" P. W. Shor and R. Laflamme LANL e-print quant-ph/9610040
This extends much of the additive LP bound to nonadditive codes.
"Quantum shadow enumerators" E. M. Rains LANL e-print quant-ph/9611001
And this extends the rest of the LP bound.