Hey Aiden,
We only support inline markup like bold, italics, underline, etc and links on guide step lines. I'm not sure if that's actually documented anywhere though.
We probably grouped comment tags along with block tags like image, embed, and code blocks that don't really fit in a small text input like guide steps. Comment tags should still work on Guide introductions, Answers posts, and Wikis. Sorry for the lack of information on that. We can probably be better at that.
