So the pointed use of a dash is all we have to do to be called brilliant? SPOGG thinks that's brilliant!
Back at the Times, longtime court reporter Linda Greenhouse cites legal praise for [Chief Justice John] Roberts' real passion, which is not modesty but punctuation. As proof, Yale professor Akhil Amar points to one line from a recent Roberts opinion: "The state did—nothing." Amar tells Greenhouse, "That little dash is brilliant."Not that we obsess about punctuation (okay, we do), but the dash here is an en-dash, not an em-dash. The en-dash is narrower — the width of a capital N. We'll let your brilliant deductive mind figure out how wide an em-dash is.
For the most part, en-dashes are pretty much exclusively used in books. Newspapers typically replace them with hyphens. When used properly, en-dashes show ranges in dates (October–December), page numbers, game scores and the like. If you want to get very persnickety, you will use it also to link compound modifiers (a Swift-Boat–style character assassination).
An em-dash shows a sudden break in thought, and is what Slate should have used.
We could not tell from source code what their writer intended, and perhaps Slate has some kooky style that bars em-dashes from their pages. Chief Justice Roberts did use one, at least according to the ruling we read here.
For that, we will give him full credit for prudence in punctuation, if not for jurisprudence.