You mean like the comment fields we're using right here on lemmy?

As others have pointed out, it's usually some markdown that's embedded within the text. Lemmy is using a format that's actually called "markdown" if I'm not mistaken, or a slight variation/subset thereof.

I've gotten used to the double-star for bold and what not to the point that it annoys me when some message client or whatever doesn't support it. I share code snippets with people fairly often, and the code markdown is particularly useful to maintain its legibility.