In the rare cases when you have a quotation within a quotation within another quotation, use double and single quotation marks alternately, like this: Bob said, “Jenny murmured, ‘Stop using ...

The single quotation mark comes after the period because that’s the rule in American English. The double quote mark comes next, because double quotation marks enclose single quotation marks.

Disclaimer: The following material may be unsettling to punctuation prescriptivists. Everyone knows that there’s only one use for single quotation marks, and that’s to denote a quote within a quote.

In general, the AP Stylebook says, quotation marks are used “to surround the exact words of a speaker or writer when reported in a story,” or, in this case, a headline.