I'm currently having an argument with several people on Twitter about this. They just cannot seem to believe that anyone has ever used the form that I've regularly heard, and they insist that they've only ever heard the technically correct form. I am . . . skeptical.
In case the question is unclear, here's an example. Let's say someone intended to write an aside in those curved punctuation marks, but they forgot the last one. You would say they left off the end or closing ______.
Cross-posted from Hiden Harbor