I’m going to say something controversial: I think the way North Americans use commas and periods within quotes is illogical. To me, it just looks wrong. If I had my choice in the matter, I would eschew it in favour of the British rules.
Let’s start with a bit of history (which I have taken from a blog post by Mignon Fogarty). Commas and periods apparently started being used inside quotation marks because of the way typesetting worked; without printing them in that way, the presses of the time would cause things to break. So, there was a practical reason for it. I assume technology quickly compensated—but, by the time it did, the use of commas and periods had become a standard.
In the early 20th century, Britain “broke” with this standard because (quite rightly, as I believe) it was illogical.
Let me briefly recap the general rules. Punctuation marks go outside of quotation marks—unless the punctuation is part of what’s being quoted, and then they go inside the quotation marks. In North America, periods and commas are an exception—they always go inside the quotation marks.
As I was growing up—and for many decades after I stopped getting taller—I used the British system (albeit with North American double quote characters). I didn’t realize until I was much older that this was wrong. I imagine it had something to do with my being Canadian and assuming I could just pick and choose from among the North American and British elements I liked best.
North American (or “inside”) style:
Commas go inside quotation marks around words like “one,” “two,” and “three,” as do periods after a final quoted word like “four.” I might also say, “So does all punctuation that’s part of actual dialog.”
British (or “inside/outside”) style:
Commas go outside quotation marks around words like ‘one’, ‘two’, and ‘three’, as do periods after a final quoted word like ‘four’. However, I might also say, ‘Punctuation that’s part of actual dialogue stays inside the quotation marks.’
(Note also the difference in the style of the quotation marks, which I included, and that I deliberately used the US spelling of “dialog” in the North American example.)
Although I can easily copyedit according to the North American standard, if I’m quoting a single word or phrase it always strikes me as wrong for it to have a comma or period inside the quotation marks because that word or phrase does not, itself, contain a comma or period.
More than that, as the British Fowler brothers claimed, it’s simply not consistent that a couple of arbitrary punctuation marks should be treated differently from all the other punctuation marks—especially when there is no justification for it.
Ironically, although I never used to find the use of commas inside quotation marks all that unusual, the more I’ve been thinking about my dislike of periods inside quotation marks, the more I’ve been struck by the inconsistency—and the more I now also dislike seeing commas treated this way.
But part of being an editor is understanding what your audience is used to. And if you want to communicate effectively, it often doesn’t matter what you prefer. It’s only when a choice can be reasonably made that your preference should be a variable in the outcome.