At WWDC apple announced that notes.app is going to support tags in the new version -- I thought that was great because while I don't use it exclusively, it's on

At WWDC apple announced that notes.app is going to support tags in the new version -- I thought that was great because while I don't use it exclusively, it's one more place things tend to accumulate. But I've been thinking a lot about tags rather than specific tools lately. I've been hoping to find prior art on how to approach tagging in a clean way. Does anyone have any suggestions? I'm seen Johnny Decimal[0] and I guess the itch I'm trying to scratch in my brain is to find a description of a way to approach tagging things which addresses the ways they can be hierarchical, and the ways they can be relational. A meta-tagging approach. It's surprisingly difficult to find. [0]: johnnydecimal.com