Rather than adding markup, when it comes to breakpoints regardless of what system the site is built with I like to add an inset box-shadow to the document BODY (assuming nothing else has done so) for each media query to colour code them, then I use generated content to add an indicator of which width trigger is active.

It's easier that way so I don't have to futz with the markup... but then things like this have no business in the markup in the first place... not that the suckers who get duped into using these idiotic CSS frameworks understand that; pissing their presentational classes all over the place and telling the separation of concerns to go suck and egg as they recreate the WORST of 1990's markup methodologies.

Ok here we go, crazy uncle Jason ranting about the evils of frameworks again...