Delegates at the recently concluded Paris climate talks worked from a draft document in which alternate wordings were laid out next to each other. For example:
Parties [shall][agree to] to take urgent action and enhance [cooperation][support] so as to (a) Hold the increase in the global average temperature [below 2 °C][below 1.5 °C][well below 2 °C][below 2 °C or 1.5 °C] [below 1.5 °C or 2 °C][as far below 2 °C as possible] …
An article in the American publication The Atlantic noted that the draft agreement contained “well over 1,000 square brackets.”
“Square brackets” is British English for what Americans call simply “brackets.” I had never encountered the expression until a couple of months who, when an English fellow remarked how odd it seemed when something I’d written referred merely to “brackets.”
“Square brackets” has appeared very occasionally in the New York Times, for example in this 2009 blog post by Jennifer 8. Lee.
My English friend also informed me that in AmE “parentheses” (like this) are “round brackets” in BrE. “Round brackets” has never appeared in the New York Times and I imagine it never will. But as Fats Waller so eloquently said, “One never knows, do one.”
[Update. Some British commenters have said that they are not familiar with “round brackets” but merely say “brackets” for what Americans call parentheses. I certainly take them at their word but the Oxford English Dictionary does have an entry for “round brackets” with British citations, including J. P. Mahaffy Empire of Ptolemies vi. 228: “Superfluous words and syllables, written by mistake of the scribe, are enclosed in square brackets. Necessary additions or corrections in round brackets.” I have also learned from my investigations that “brackets”/”square brackets” were formerly called “crotchets.”]