Comment 5 for bug 170922

This feature is more interesting and powerful than you expect: once you can make objects dependent on each other by gluing them, you get geometric analysis. So you can do fun stuff like this:
http://upload.wikimedia.org/wikipedia/commons/8/88/Geogebra9pointcircle.JPG
http://rdassonval.free.fr/geogebra/rcdiapoorthocentre.jpg
http://rdassonval.free.fr/geogebra/cercles.jpg

You can move a node and the rest of the diagram will morph to accommodate it. More elaborate diagrams result in more fun. It's very useful for geometry in math olympiads, where objects are glued in dependencies that are 20 or 30 objects deep.

Any gluing model would basically be an acyclic directed graph of dependencies.