"It's a 'nurse's' pocket...Essentially, it’s a loophole for manufacturers to bring costs down. 

If garments have 'pockets below the waist, a ribbed waistband or other means of tightening at the bottom of the garment,' they get excluded from specific categories. So if you took that same type of blouse with a 26.9% duty rate and added a pocket or two below the waist, it would instead get tariffed at a rate of 16%."