One of the best puzzles around...
Have to diagram it - multi-dimensional tree structure (or can model as concentric circles).
Object types, User Groups, Domains (Org / Product) are all like this.
If you assign some permission to WTDocument, it applies to all sub types. In general, to make an exception, you have to remove a subset such that it stands alone - as a Private context, or a group not within a group, or an object type parallel with another object type.
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