Maybe is for this (in red color, copied from Qlik help):
GetFieldSelections- chart function
GetFieldSelections()returns astringwith the current selections in a field.
If all but two, or all but one of the values are selected, the format 'NOT x,y' or 'NOT y' will be used respectively. If you select all values and the count of all values is greater thanmax_values, the textALLwill be returned.