This is when we have those double quotation marks, don't miss a single word, and cite the person who made the statement.
这时，我们要使用双引号，不要漏掉任何一个词，并引证说出这句话的人。
牛津大学：英语写作专攻课
Generally, we recommend using double speech marks to quote what someone said, and single speech marks for everything else.
通常，我们建议使用双引号来引用某人所说的内容，而在其他所有内容中使用单引号。
英语百科
Double-marking language
A double-marking language is one in which the grammatical marks showing relations between different constituents of a phrase tend to be placed on both the heads (or nuclei) of the phrase in question, and on the modifiers or dependents. Pervasive double-marking is rather rare, but instances of double-marking occur in many languages.