To formalize they are now XML-compliant (with some asterisks.)
Also to help syntax highlighters work on them to make their content more
readable.
Also:
- Delete empty comment decorations.
- GHA/checksrc: simplify XML check.
- runtests: fail to load test data with XML prolog missing.
Follow-up to bfe6eb1c06#19927
Follow-up to 87ba80a6dfCloses#19946
There remain some false positives, hits in test data, and `dir` use,
around 100 issues in total.
There is no plan to enforce badwords on tests.
Also:
- badwords.txt: let a few `manpage[s]` occurrences through
(in Perl code).
Closes#19541