Uh, I think he means that he can see and arrange notebooks on his computer screen, and nest them. They take up a spot in perceived and visual reality, like putting things in a file cabinet and folders, instead of just going around the office, and marking the stuff with tags, then maybe having various lists of the tags that he can look at and search. Some have great spatial memory, not for lists. He said that was how he perceives things, and he might be really good at it. He said that tags seem to be abstract to HIM. By abstract, he means that they do not have a position in space that they occupy. They are not an object that can be positioned, etc. He did say that is how HE perceives it. Windows had folders that nest, and that is what many people are used to, surely. Maybe it was wrong. Don't know. So, tags give a way to cross reference items in all file cabinets and folders whether related or not, but many still want their file cabinets in a building of multiple offices, in an office area with multiple rooms, in a filing room with multiple cabinets, in a file cabinet with many folders, in a folder with many notes, and some of those notes are clipped together.. Spatial. The items exist in space. They have a specific location. (By the way, I'm thinking that the folders we see in the UI, only appear to exist, as simulated by the UI, but they do APPEAR to actually exist.) meanwhile, back onto the subject of nested notebooks ...