em dashes: with our without surrounding spaces

[frivoal]

https://speced.github.io/bikeshed/#typography tells us:

Ending a line with -- will turn it into an em dash (—) and pull the following line upwards so there’s no space between the surrounding words and the dash.

in https://github.com/w3c/w3process/pull/851#discussion_r1567542467, @tallted said:

Ugh. In my world, em dashes should be surrounded by spaces; en dashes and hyphens typically should not.

The W3C Style Guide points to the Chicago Manual of Style, and "CMOS says no spaces, but importantly their typography actually does have spacing around the em-dash, so basically they’re cheating a bit. AP says spaces."

I don't care strongly either way, but I'm pretty sure that if it should be fixed, it should be fixed globally, and not on a ad hoc basis. Hence reporting it here, as well as against the W3C Style guide.

[TallTed]

Visual examples — like this, with the surrounding spaces — are often helpful. You can see here that the surrounding spaces help suggest the separation intended by the em-dash.

I think this—lacking the spaces—looks cramped, at best, and visually decreases the separation intended by the em-dash (as opposed to en-dashes or hyphens, which are meant to connect, as in ranges, like 5–10, or in compound words, like en-dash).