dd on English Wikipedia talk pages have extra top and bottom margins.

https://en.wikipedia.org/w/index.php?title=MediaWiki:Common.css&oldid=1369120317#L-36--L-40

/* Same spacing for indented and unindented paragraphs on talk pages */
.ns-talk .mw-body-content dd {
	margin-top: 0.4em;
	margin-bottom: 0.4em;
}

Hmm. Interesting. OK, that's the root cause. I'm not in .ns-talk on the page I linked in the ticket.

So dd margins aren't built into MediaWiki core? So if I'm not on an English Wikipedia talk page and I want the line break to be visible, I should write code like this?

:Test

:Test

What about when I type the following into DiscussionTools in visual mode or in source mode?

Test

Test

DiscussionTools writes the following wikicode in both visual mode and source mode, erasing my line break.

:Test
:Test

Hmm. I'm not sure exactly what direction to go in, but it feels like there's a bug here somewhere.

I've posted https://en.wikipedia.org/wiki/MediaWiki_talk:Common.css#Line_breaks_between_paragraphs_missing_on_noticeboards to explore fixing this on the enwiki side.

In T436428#12268003, @Novem_Linguae wrote:

Hmm. Interesting. OK, that's the root cause. I'm not in `.ns-talk` on the page I linked in the ticket.

So dd margins aren't built into MediaWiki core? So if I'm not on an English Wikipedia talk page and I want the line break to be visible, I should write code like this?

:Test

:Test

Please don't leave a blank line between list items that are within the same list hierarchy. This closes the first list and opens a new list, which causes screen readers to make extra list end/start announcements. It also can lead to the visual diff capability highlighting supposed changes that aren't actually changes.

My downstream Common.css patch got merged, so this ticket is solved for the time being. I will mark it as resolved.

Isaacl makes a great point about screen readers.

I've gone ahead and filed T436439: there should be visible space (margin) between paragraphs indented in wikicode using a colon to explore the broader issue of upstreaming the Common.css fix and fixing this for all wikis, in a way that doesn't break accessibility.