http://www.thepunctuationguide.com/british-versus-american-style.html
The above examples also show that the American style places commas and periods inside the quotation marks, even if they are not in the original material. British style
(more sensibly) places unquoted periods and commas outside the quotation marks. For all other punctuation, the British and American styles are in agreement: unless the punctuation is part of the quoted material, it goes outside the quotation marks.