The hemline on the miniskirt is changing again. And since they can’t get any shorter (or can they?), they’re getting fuller — this time with a bubble hem. Costello Tagliapietra gathered her hem on a dip-dye skirt; Donna Karan added a briochelike touch to several pattern dresses; and Hervé Léger used the bubble hem to deviate from a collection of second-skin dresses. Feeling bubbly yet? —Sharon Clott