Page "Comparison of American and British English" Paragraph 23

* Quotation usage: Americans almost always place commas and periods inside adjacent quotation marks.

Specific exceptions are made for cases in which the addition of a period or comma could create confusion, such as the quotation of web addresses or certain types of data strings.

In both styles, question marks and exclamation marks are placed inside the quotation marks if they belong to the quotation and outside otherwise.

With narration of direct speech, both styles retain punctuation inside the quotation marks, with a full stop changing into a comma if followed by explanatory text, also known as a dialogue tag.

Americans tend to apply quotations when signifying doubt of veracity ( sarcastically or seriously ), to imply another meaning to a word or to imply a cynical take on a paraphrased quotation, without punctuation at all.