Noguchi Yukio, an economist and writer of bestselling books about such things.
Implementation of the system requires the user to discard many conventional
notions about how to store paper documents.
some means for marking the outside of the envelope. If some color coding
(optional) is to be done, this can be done with marker pens.
perceived chance of being required at a later date are stored in A4-sized
envelopes, which have the flaps cut off… By "all documents," Noguchi means just that. He puts all categories of
documents, including things like membership lists and his passport in envelopes."
The Noguchi Filing System
By William Lise
[via Rebecca’s Pocket]