To continue the over-analysis in good faith: I think the trashcan example points out the inheritance of draggability. Any file object in a directory gets it by default, without having to think too much about it.

Then the trashcan inherits from a directory, making it able to have things dropped on it. But it overwrites the action taken from movement to deletion. That maps "nicely" onto the human mind.

> If anything, you're invoking the environment's "drag" function with two arguments, "document" and "trashcan";

A perfectly valid alternative description. But having a do-it-all environment with every function doesn't sound OOP to me.