Router state
A router state is a subtree of the configuration tree. For instance, the example below has ConversationsCmp activated. We say activated instead of instantiated as a component can be instantiated only once but activated multiple times (any time its route's parameters change):
Not all subtrees of the configuration tree are valid router states. If a node has multiple children of the same color, i.e., of the same outlet name, only one of them can be active at a time. For instance, ComposeCmp and PopupMessageCmp cannot be displayed together, but ConversationsCmp and PopupMessageCmp can. Stands to reason, an outlet is nothing but a location in the DOM where a component is placed. So we cannot place more than one component into the same location at the same time.
