20. An article as in claim 19 , wherein categorization of each provided document by the user-generated input is propagated to all documents within the corresponding stack.
20. An article as in claim 19 , wherein categorization of each provided document by the user-generated input is propagated to all documents within the corresponding stack. 22. An article as in claim 20 , wherein at least one documents is incrementally added to the document set after the grouping of the plurality of documents into the plurality of stacks, and wherein the operations further comprise: determining that the at least one incrementally added document is not associated with a previously defined stack; and defining a new stack including the at least one incrementally added document.