Square brackets "[ ]" indicate that the text inside the brackets is optional OR that one should consider whether the text inside the brackets should be edited. Bryan Garner who is the leading prescriptive guru on legal writing says in Legal Writing in Plain English: "Use a pair of brackets in a quotation to enclose an editorial comment, correction, explanation, interpolation, substitution, or translation that was not in the original text." In other words, they can be considered the legal equivalent of saying "optional/ignore in final document version" when used.