Concepts
	basic
		item
		| a basic element in the system.
		| an item is represented by a URL
		group (item)
		| a special item that unifies several items
		list
		| a representation of several items
		tag
		| a piece of text connected with an item
		action
		| a user defined command or script
	constructed
		state (tag)
		| a named state of an item
		stack (group)
		| a set of versions or states of an item
		| a stack behaves like an item
		collection/list
		| a special list defined manually or with a search that is maintained in the filesystem
		tag chain
		| a special tag that consists of several tags
		event
		| a condition that can be bound to an action
		workflow
		| a named sequence/graph of states and transitions (actions)
	structural
		store
		URL
	

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