What one openable row of the wave selector stands for, which is both how it is styled and the key under which the model remembers whether it is open. A row is a group of components within one sheet instance, or the sheet instance itself. There were also cases for a single component and a single port, from when the list was nested a level deeper than it is; nothing has built one since, so the rows that would have used them are gone and only their styling and their summary text remained.