Mediawiki how they load skins and extensions as of 1.25. Many of our extensions use the new format, but Neverland hasn't been updated to conform to this.
A guide: https://www.mediawiki.org/wiki/Manual:Extension_registration#Migration_for_extension_developers
Have you sent the right link?
However, I'm consciuos of the fact that Neverland is not using semantic tags. Let's think about what should be done and if it should be done. We have a plan to reskin the entire Nverland, writing it from scratch due to its brokeness so if this task doesn't affect much the entire system, I will delay adn assign it when the new skin will be built.
Instead, if this is to be take into account on Nverland, what kind of tags (in addition to HTML5 tags) should be used?
That is a good idea. It shouldn't be necessary, and if it is being rewritten soon, then it can be done there. It is mostly just a semantics issue, not so much a functionality one.
About the link....The documentation is pretty bad and the one about extensions mentioned skins a little bit, which was the best I could find.