Constrained Creation: A Folder Structure from 3 Rules

Task: design a folder structure, at least two levels deep, to hold work documents (or personal files). But you may not make the folders first. Make the rules first, and let the rules give birth to the structure.

Make 3 rules of your own that decide the folder structure (e.g. rules about naming, classification criteria, depth limits, retention periods). Then, using only those 3 rules, design the folder structure as a tree (at least 2 levels, 8 or more folders). Your answer must include (1) the 3 numbered rules, (2) the folder tree, and (3) the process of judging, by the rules, which folder two new-document examples go into (e.g. a client contract, a meeting transcript).