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Writers frequently debate whether or not the Oxford comma is a necessary piece of punctuation.

In an unlikely turn of events, a group of Maine dairy drivers have yielded the answer: Yes, it is.

A case brought by the dairy drivers against Oakhurst Dairy and Dairy Farmers of America Inc. about whether or not they qualified for overtime hinged on the lack of a comma in a sentence outlining duties that were exempted from overtime pay.

On Monday, a federal appeals court judge ruled in favor of the drivers after finding that the lack of a comma dredged up so much uncertainty: “For want of a comma, we have this case.”

Oakhurst dairy plant in Portland on June 17, 2013. Jill Brady / Getty Images

The use of the Oxford comma — also called a serial comma — delineates the final item on a list. For example: "Milk, cheese, and yogurt." Proponents of the punctuation argue it helps to differentiate subjects, while opponents say it’s cumbersome.

Different style guides have different rules about the Oxford comma, which gets its name because it was used by Oxford University Press editors, but the judge’s ruling is a cautionary tale for those who forgo the mark.

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The sentence at the heart of the dairy drivers' case refers to Maine's overtime law and whom it doesn't apply to: “The canning, processing, preserving, freezing, drying, marketing, storing, packing for shipment or distribution of:

“(1) Agricultural produce;

“(2) Meat and fish products; and

“(3) Perishable foods.”

Because a comma does not appear after “shipment,” U.S. Court of Appeals for the First Circuit Judge David Barron reasoned it is unclear if "packing for shipping or distribution" is one activity or if "packing for shipping" is separate from "distribution."

“The drivers further contend that, although they do handle perishable foods, they do not engage in ‘packing’ them,” Barron wrote in his opinion. “As a result, the drivers argue that, as employees who fall outside Exemption F, the Maine overtime law protects them.”

Ian Samuel, Climenko Fellow and Lecturer on Law at Harvard Law School, says at least one prominent legal text, written by Justice Antonin Scalia and his co-author, Bryan Garner, recommends that "courts should not rely much if any” on text omitting an Oxford comma because some legislative style guides follow newspaper style, which often doesn't use the comma.

In Maine, the guide for drafting legislation warns against using an Oxford comma, as Barron notes in his opinion.

“Although authorities on punctuation may differ, when drafting Maine law or rules, don’t use a comma between the penultimate and the last item of a series,” the rule reads.

However, it also warns that if a list is ambiguous, a sentence should be restructured.

"The reason the lack of a comma matters here is because it’s not clear if the overtime statute is supposed to exempt packers of food — those whose work involves the 'packing for shipment or distribution' of perishable foods (which milk is) — or if it covers both packers (people who 'pack for shipment') and drivers, whose work is the 'distribution' of the foods," Samuel said in an email to NBC News.

Samuel says the key to this case isn't ultimately about the text, but rather that because the exemption is ambiguous, there isn't a clear-cut answer.

"The court concludes that at best the phrase is ambiguous. In other words, the text by itself just doesn’t tell us the right answer syntactically," Samuel said. "So we have to rely on a substantive presumption in favor of workers, which the court says is used in Maine law to resolve ambiguities like this."

He said it's conceivable that a different judge could come to a different conclusion.

"This opinion by Judge Barron is very carefully argued, and I personally think it’s really good," Samuel said. "And he is a very well-respected judge. That said, it’s not an open-and-shut case. I think it’s actually a pretty hard one."