In the previous chapter, we argued that a modular design
and corresponding task structure make possible a particular
type of industry structure, called a "modular cluster". In
a modular cluster, the tasks of desinging and producing the
different parts (modules) of a complex artifact are spread
over many different firms. The firms' activities are
coordinated by design rules that govern key parameters of
the artifacts' design. Conformance with design rules is
meant to ensure that modules produced by different firms
in the modular cluster will work together as functioning

Design Rules, p. 383.