Do you think it's a good idea to define what happens for ! each?
Currently "each" will put for each input value exactly just one output value into the list of the results, effectivly deleting duplicates.
Currently "!" is not defined for each.
So why not use it for finding duplicates? Stupid idea, maybe, but maybe usefull?
<$list filter="[[test]] [[test2]] [[test]] [[test3]] +[each:value[]]">
-- will give you test, test2 test3
<$list filter="[[test]] [[test2]] [[test]] [[test3]] +[!each:value[]]">
-- would give you test
Tell me that it's a stupid idea ;)