I recently found this fascinating story of a legacy of typesetting that still creates a difference between American and British punctuation. Proofreaders have to stay mindful of it when dealing with American conventions.
In the past, compositors (people who lay out printed material with type) found that the small pieces of type would not break off the end of a sentence, so the full stops (periods in the US) and commas would not break off either. For this reason they made the rule that made the rule that full stops and commas had to be placed inside quotation marks. This rule became the convention for how to place commas and full stops in regard to quotation marks.
Then, in the 1900s the Fowlers Brothers campaigned for full stops and commas to be placed outside quotation marks, except for direct speech. This was so the grammar rules would follow logic rather than typesetting convenience. This new rule was adopted for UK English. Its advantage is that placing the full stops and commas outside quotation marks makes it clear that what is inside the quotation marks is a quote or highlighted word and not direct speech.
However, the US did not adopt the rule change. So to this day, UK English follows the rule that full stops and commas go outside quotation marks except in direct speech e.g. “That movie was terrible,” said Mark. But US English, they still go inside.
(US English) I can never remember how to spell “ecstasy.”
(UK English) I can never remember how to spell “ecstasy”.
This rule applies only to full stops and commas. In both UK and US English all other punctuation, such as semicolons, colons and dashes, always go outside quotation marks. Moreover, some American-based conventions, such as the APA reference style, have adopted the UK rule of full stops and commas outside quotation marks in order to differentiate highlighted words and quotes taken from sources from direct speech.