Any time a topic makes use of a key reference, that topic is explicitly binding itself to a map (or many maps), meaning that a topic is no longer a unit of information that is completely independent of any particular context in which it is assembled into. You could make the argument that any reference defined in a topic to an external resource (e.g., an image or a cross-reference to another topic) by definition creates a dependency on that topic. And arguably, the referenced (the endpoint) resource is unaware of the object that is referencing it, regardless of whether it's a topic reference or a cross-reference. But there is an additional dependency in the case of keys: Any map that references a topic with a key reference must define the key. So in a sense, not only does the map (or an ancestor map) need to know about the topic, it needs to discover what the topic is about, specifically related to any key references it points to. Consequently, somewhere along the line, at least one map must define the keys used by a topic. Did you get all that? Imagine what your XML authoring tools, CMS systems, and rendering platforms will need to do to manage this.