Re: Box brackets
The use of these square brackets is to insert what was meant in a quote, even if it was not what was actually said.
For example, the person is speaking or writing about someone named John Smith but in the part you want to quote, he just says "he." When you quote, you insert "[Smith]" instead of "he" so the reader knows who is being referred to.
You can also do it to correct a mistake.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.