[tzot]

I always have been using em-dashes with specific spacing:

1. replacing parentheses —given that the em-dash in pairs for me mark more-relevant-to-the-main content than a parenthesized expression would— so I use the same spacing as `()`

2. replacing colon or just finishing the sentence with a subsentence— so the spacing goes like for a colon.

Probably unfounded grammatically and against any style guides, but this spacing makes sense to me.

[estebank]

I am pretty sure an em-dash in case 2 should not have spaces in either side.