I love how in the first page of chapter 2 they specify the distinction of files in two classes: shareable and variable. Then they specify that files which differ in any of these two properties should belong to a different root folder. Then they go ahead and give you an example which clearly explains that /varshould contain both shareable and non shareable files.

Good job with your 4 categories, I guess that’s why nobody really understands what /var is…