VE error: The modification you tried to make was aborted by an extension hook
Source editor error:
Translation unit markers in unexpected position. Translation unit text: <!--T:83-->In general it is preferred to share code via composer components instead of extensions. If the classes of an extension only need to exist, but the extension does not need to be configured nor loaded, for what you want to do, that is a strong indicator that that code should be split off into a composer component you should depend on instead.
Found during https://www.mediawiki.org/w/index.php?title=Manual%3AExtension_registration&type=revision&diff=1974486&oldid=1974468 .