Furthermore, the conventions for the first (parenthetical) use case, as far as I understand, are either em-dash without spaces (Anglosphere convention), or en-dash with adjoining spaces (Continental convention: German, French, etc.), but rarely em-dash with spaces (as in the article).
> em-dash with spaces
my favourite (and I hope LLMs never converge to use it)
Isn't that what they predominantly use? I don't think I've ever seen an LLM use an em-dash without spaces. I've never seen an en-dash with spaces, but have seen them in ranges.
I checked a message from my last chat with Claude
> Noted for this conversation — though worth flagging
and that's an em-dash (unicode 0x2014)
A spaced en-dash is also commonly used in British english for the parenthesis equivalent. So it's not really "anglosphere".
While there's no central authority, both Oxford and Cambridge University press style guidelines recommend that.