Tags in TagTree are defined in a tree-like structure, and you can check if an object has a tag on any level of the tree, meaning that if a character has a tag "State.Stunned.Electric" and you want to check if the character is stunned, you can simply check for "State.Stunned" instead.
Basically anything can have tags, you just need to create an object of type TagContainer, but there's already a built-in extension specifically for GameObjects, so you can just use that straight away!