[stouset]

Since we’re being pedantic, canonically you aren’t supposed to separate an em dash with spaces. I assume that’s because typographically it already sets the parenthetical somewhat farther apart than a regular space would.

“Through the window she saw George—a policeman—and several onlookers.”

[wolverine876]

> you aren’t supposed to

In the world of grammar, these words are always a shot at your own toes. I'm missing a few myself and I learned: always specify a domain or a source.

The AP Style Manual, the bible of grammer for journalism (at least in the US), says to put spaces around the dash. However,

https://news.ycombinator.com/item?id=39436513

[xeonmc]

No, there should never be spaces around Em-dashes, while for En-dashes they are situational---spaced if being used in lieu of Em-dashes, and unspaced if used as ranges (e.g. 1938--1945) or comparisons (e.g. Blue--Red Dichotomy)

[wolverine876]

What basis do you have for saying that, and for refuting the AP Style Manual? Are you claiming it says otherwise?

[xeonmc]

You might be unaware that there are three types of dashes. For grammatical connections, you choose only one of the following and stick with it

- Em dash: unspaced

- En dash: spaced

For relations, it is always unspaced En dash

[wolverine876]

Do you see what I'm writing? Does it seem I'm unaware? There are even more such marks.

Still no source for your claim. Why do you think these things are true, and that always flawed claim, universally true?