Trees can point upward too. There's incoming references. There's metadata tags/facets. And there's multitrees, that might or might not help. https://interacti

Trees can point upward too. There's incoming references. There's metadata tags/facets. And there's multitrees, that might or might not help. https://interactivity.ucsd.edu/articles/In_Process/MultiTrees.pdf https://interactivity.ucsd.edu/articles/In_Process/MultiTree...