When quoting a source, brackets are typically used to signal that the quotor† has modified the original material.
But what if one is quoting a source that has itself quoted a source? How do you eliminate ambiguity as to who added the brackets? And then, what if the first quotor has already added brackets, and the second quotor wants to add its own too?
This isn't a purely academic question, since I'm asking this from the perspective of legal writing (where minutiæ like this might actually matter‡).
I think different color brackets would be a neat solution, especially when you got into levels of bracketing beyond two. Unfortunately color printing availability and cost would be prohibitive. Any other suggestions? (At least for the two-level scenario?) Perhaps a clumsy parenthetical sentence along the lines of (First brackets in initial quotation, second brackets added.) ?
† I used the -or suffix over the -er suffix because quote is of Latin origin. I hope you're impressed.
‡ That reminds me—tomorrow at work I have to find this "awesome" case where the court decides that and means or. Note to self.