Let's say you are a reporter and keep statistics of crimes in your city. Murders, robberies, car thefts - for each type of crime, you add a corresponding tag. You also add additional tags to your notes: names of lawyers, judges, acquittals, etc. All these tags are combined into the "yourcity _crimes" tag group. This is a convenient way to structure data and cross-tag information to find the information you need. And now you want to look at the general situation in the city ... but no. An effective tagging system and its versatility is why I have been with EN for ten years.