While he doesn't treat the subject exhaustively, there is a section on enlargement, with which I have more than a passing familiarity.
This is speculation on my part, but because cold-light enlargements match the tonal scale of contact prints, Zone System concepts can be demonstrated with either type of image. Indeed, the book contains examples of both.
Some of the illustrations are contact prints from strips of roll-film. Perhaps it's mere coincidence, but exposing, developing and printing at the same time eliminates several variables: only the fundamentals remain. I would be surprised if that wasn't done intentionally.
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