Cartoon demonstrating the two proposed mechanisms responsible for the transition disk cavity appearance. For disks classified as Group A it is thought that one or more Jupiter-like planets with a mass well above the pebble isolation mass have carved a gas gap, trapping the millimeter dust in a narrow ring outside its orbit, whereas for disks classified as Group B a number of Neptunian planets with a mass below pebble isolation mass are still actively accreting pebbles, thereby creating the appearance of a dust cavity as the inner edge of the dust ring is acting as a ‘filter’ where pebbles are accreted, and the pebbles in the dust ring are not trapped, but follow a smooth dust density pattern.