Only punctuation marks that are directly part of a quote should be placed inside the quotation marks. Any other punctuation marks should be placed outside and after the quotation marks. No punctuation that is part of the quote (thus, inside the quotation marks) should be used to help construct the editor’s sentence structure.
For example, let’s say a person says, “I have many cars. This is a red car. That one is a blue car”. Another person then quotes part of what the first person said by writing, “This is a red car.” and includes the period before the ending quotation mark like I have shown, should be deemed a correctly structured sentence. The editor could also write, “This is a red car” without the period and it would still be correctly structured and quoted because it is the editor who could pick what he wants to quote (where to begin and end a quote), so long as the original message is not adulterated. An editor quoting this same sentence at the end of his own sentence would write it to appear like this: “This is a red car.”. or “This is a red car”. The editor could decide whether or not he wants to include the final period in the original quote. Adding a period within the quote in this example would be redundant, but there are situations where either the quoted punctuation mark or the editor’s punctuation mark after the quote would be different and thus convey a significant or essential meaning to the reader as illustrated in the following sentence: The man said, “This is a red car!”.
Is summary, the British style of punctuation should be used in America and everywhere else the English language is used.