Lesson six of a course on holding the model while an AI does the work, for anyone unsure how much to write in a brief. The idea is David Parnas’s (On the Criteria To Be Used in Decomposing Systems into Modules, 1972): specify a module by the interface others may rely on, and hide its insides so they are free to change. The band between too vague and done-in-prose is this course’s framing.