In the Swedish category is question about grouping archipelagos. I answered and said using a relation is not a good idea. (list all islets in a relation. Relations are not categories - OpenStreetMap Wiki)
But on the wiki page about archipelagos Tag:place=archipelago - OpenStreetMap Wiki it says you should/could list islets in one and same relation!?
relations are not categories, but for an archipelago they seem a good fit, not?
What I meant to say: putting all islands of an archipelago in a relation is not abusing them as „category“ in the wiki sense of the word, a category means a generic type of thing like an island or an archipelago, not a specific archipelago
Yes this seems like standard tagging for a named archipelago. For example the Balearics, Canaries, Azores, and Cape Verde islands are all tagged in this way (sometimes on the same object as an administrative unit that happens to cover the same group of islands). Noting the points on the place=archipelago wiki about very large relations or very widely dispersed island groups, the suggestion seems OK.
I think the rule against using relations for categories would apply to something like “all archipelagos in Sweden” or “all islands in Sweden that are part of an archipelago” or “archipelagos of Europe”. But the mapper who asked the question wasn’t proposing anything like that.
All islands or islets forming an archipelago are a geographical objekt and not a category.
Thus they can (not must) be grouped into a relation.