I think it's meant to promote looking at how a literate programming system is mangling program output. It's way more complicated and powerful than just "inverte

I think it's meant to promote looking at how a literate programming system is mangling program output. It's way more complicated and powerful than just "inverted comments" (like e.g. CoffeeScript did in recent memory). Composite parts of the final program can be presented out of order, sent to different output files, etc. For something slightly more modern than this sample program or TeX, there's "A Retargetable C Compiler: Design and Implementation", which presentes the code of lcc, a quite conformant C compiler (which, IIRC, still enjoys some popularity on Windows). Sadly the strengths of literate programming are rarely useful for mere mortal programmers -- we're not often entrenched in deriving algorithms and/or presenting something in a didactic manner.