Brackets are used to enclose editorial interpolations, corrections, explanations, or comments in quoted material.
Resist the temptation to use "[sic]," which in Latin means "that's your mistake, fella, not mine," to point out a mistake in a quotation. Instead, try to fix the problem in the quoted passage.
"This law does not apply in our grate [sic] state."
Better: "This law does not apply in our [great] state."
"He used the name e. e. cummings [sic]."
Notice that inserting bracketed material does not prompt a need for the "ellipsis signal": three dots used to show omission.
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