Thread:BunsenH/@comment-26228416-20160904031630/@comment-24577221-20160904044157

You mean the highlighted box around some text? It's something the wiki does when text is edited in Source mode and a line begins with a blank.

I don't know if there's another way of doing it. I think it's supposed to be for things like pieces of computer code, where it's important that text is formatted exactly the way it was originally written. No automatic line breaks, text is formatted in a monospaced font to preserve alignment, etc.