Uh oh, that’s incompatible with standard em dash usage, which is with no surrounding whitespace.
(I’m designing a lightweight markup language of my own, and it’s tempting to special-case an em dash at the end of a line that is not preceded by a space, to join to the next line without inserting a space, but I’ve been trying to avoid nuance in rules. But I definitely do want to put line breaks after em dashes sometimes.)
Though I prefer the spaced en dash myself, and I am in the UK, I think there's probably a lot of variation on both sides of the Atlantic.
-->like this. I'm okay with that because there are some edge cases [1] in CommonMark that I absolutely need to use one anyway.
[1] https://talk.commonmark.org/t/foo-works-but-foo-fails/2528
But in that case I would prefer that the source text still has no spaces. Such things can be added in postprocessing.
> 3. A semantic line break SHOULD NOT alter the intended meaning of the text.
That should be #1 MUST NOT
Adding a semantic line break inherently changes the relationship between words, and we can't always be sure about the intended meaning of text. If this were MUST NOT, then any modification would risk violating the spec.
Then again, this may be my own, idiosyncratic reading of RFC 2119. If you'd like to discuss this further, feel free to open an issue on the GitHub repo here: https://github.com/sembr/specification/issues