From my knowledge, ((its emphasis!)). So the more brackets, the more its emphasized over others in the prompt (i think). Im not 100% sure what {} mean, maybe its the same?
But for 300 renders this is pretty awesome honestly.
U can even do things like details for tags, such as....
multicolored hair:<(black hair), red hair>
cat tail:<tail raised>
That sorta thing.
Good luck with your future renders~! Hope to see sum on here :3