The way I learned, which I think is close to 'British' English, is that single quotes ('..') are used to quote something that has been paraphrased (is not verbatim), is not complete, or is just being put in quotes for emphasis. Double quotes are used "...to quote word for word a sentence, passage, or entire treatise in the middle of another body of written work."
Does that sound about right? What is the 'American' way?
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