The problem is that '!node' bundles together a couple of different unrelated functions (whether the node shows up in the callback, whether the node is executed before other nodes, etc). 

I'm trying to tease those unrelated functions out by coming up with new names for things.

So for example, this input validator has nothing to do with node ordering. The only reason it's separate from ArgumentInputValidator is because it doesn't pass on the values to the next callback.