The filters worth offering: those that leave something to show and
something out, and that show a set of objects no earlier filter already
shows. A filter matching every object changes nothing, one matching none
would open an empty list -- a trap for a keyboard -- and two with the same
members, "Level 2" and "Leaves" on a two-level tree, would make the reader
step through one list twice. The earlier of two such filters is kept, so a
chart lists the more specific wording first.
The filters worth offering: those that leave something to show and something out, and that show a set of objects no earlier filter already shows. A filter matching every object changes nothing, one matching none would open an empty list -- a trap for a keyboard -- and two with the same members, "Level 2" and "Leaves" on a two-level tree, would make the reader step through one list twice. The earlier of two such filters is kept, so a chart lists the more specific wording first.