I have redone my UI concepts. A dockable panel now is "just" a notebook. This works out much better. Before I was adding lots boilerplate to slice a top level notebook into pieces that were manually placed. It was hard to program and very fragile. Furthermore, it was hard to navigate the module structure of notebooks. This new way is much better. A whole lot of concepts are removed, but also, I think notebooks tend to explain what they do within the notebook, so you end up learning about the orthogonal components in a more approachable way, plus the whole concept of a module structure manifest to the UI in a way that encourages learning. The entire concept of a top level notebook kind of disappears altogether as well, which is closer to what the serialized and runtime format is. You can have circular imports in Observable, there is no "top" at the runtime level, its a graph of reactively cooperating modules. The UI now reflect that properly. I've mapped the nested docker layout structure to the hash URL so the view layout can be saved and hyperlinked, and in HTTP terms is a pointer to a specific part of the cooperating module graph. I will add the ability to set a default layout if no hash is found, and that kinda servers the purpose of pointing to what the intended purpose of the assembly is (a role previously fulfilled by having a single top level notebook).