How do you use quotation marks with other forms of punctuation?

Webster's New World Dictionary states the comma and the period are always enclosed within the quotation marks. The exclamation and question marks are placed within if they apply to the quotation and placed outside if they apply to the whole sentence. Example: "I'm leaving," he said, "but you may come with me." "Can I go too?" she asked. Didn't I say, "you may come with me"?