That page is prepared using two TXR programs, which happen to be checked in side-by-side:

Suck down the data, print it in a condensed format on standard output:

https://www.nongnu.org/txr/fetch-txr-solutions.txr

Generate pages with frames from above data:

https://www.nongnu.org/txr/make-pages.txr

The workflow is to fetch the solutions into a new file and then to use a text merging tool like meld to update the stable copy.