Let me give you an example.

#module eggs

eggs_var = 0 # a variable, maybe a counter or similar
EGGS_CONST # a constant

#module spam

import eggs

spam_var # Another variable

def foo():
    use(eggs.EGGS_CONST)

-------------

We will want to treat `eggs.EGGS_CONST` as a constant.
To do that we need to be notified if `spam.eggs` or `eggs.EGGS_CONST` changes, but we do not want be notified whenever `spam.spam_var` or `eggs.eggs_var` changes.

This might not be necessary for us right now, but we will want to implement optimizations over larger regions than a single bytecode in 3.12.