  The formal weight enumerators were first introduced by M. Ozeki, and it was
shown in the author's previous paper that there are various families of
divisible formal weight enumerators. Among them, three families are dealt with
in this paper and their properties are investigated: they are analogs of the
Mallows-Sloane bound, the extremal property, the Riemann hypothesis, etc. In
the course of the investigation, some generalizations of the theory of
invariant differential operators developed by I. Duursma and T. Okuda are
deduced.
