Loosing? Learn the English language, people!

In reply to @Oliver Schick

The NYT and New Yorker style guides are bonkers ("coöperate", "D.J.-ing" for example), but this is all about personal taste imho.

I don't know. There are just various ways of separating non-diphthong vowels. A trema to my mind should only be used for different vowels, e.g. Haïti. Another problem with it is that it has different functions in different languages, e.g. in German it's *not* separate from the letters A, O, and U in Ä, Ö, and Ü—these are whole letters, or "Umlaute"—the diaresis is not the Umlaut/'umlaut', that's the whole letter. The hyphen in co-operate etc. is therefore a much better option. (I generally think that for most English compound nouns, which in English are generally not drawn together, hyphens are the preferred way of indicating the unity of the noun. Exceptions apply, but for clarity I think that's the best way.)

The more style guides I've read, the more I've realised they're just conventions, dictated more or less high-handedly depending on the author/publication.

I haven't read too many, but found plenty to disagree with in every single one I've seen. It's a terribly confused situation in German since the ridiculous spelling 'reform', which has left generations adrift.

I prefer no space if an em dash is after interrupted speech, it's between two dates, measures etc, or it's being used to balance out two mirrored clauses (man proposes–God disposes), but I prefer a bit of space when it's occupying a similar function to a regular dash.

Isn't that's an En dash you've put there?

Yikes. Really didn't realise I had such depth of feeling about em dashes.

Why not, if you're professionally concerned with them (as I guess you are)? (It should always be 'En dashes' and 'Em dashes'.)