Passing data up the render/box tree

[lazingor]

Is there a way for an Atom to store some data at the top level of the box tree (or somewhere), in the createBox() method?

Basically, I have a custom macro that creates a custom Atom, and I want that atom to add some data (say a string) to some top-level object, whether it's the very top atom of the tree, or the TeXEnvironment, or a TeXRender object, in a way that can be exposed to other methods, but I can't quite see what the best way to implement it is. Any suggestions?