related: #2652 #2653
I found more.
https://www.domjudge.org/docs/manual/8.3/problem-format.html
https://www.domjudge.org/docs/manual/8.2/index.html
The above link wrote: The base of the format is the ICPC problem package specification. with a broken link which is fixed on main document.
Seems that a patch needs to be applied to older documents.