Another question I have is why does node_invoke exist if module_invoke_all does the same work? Does using node_invoke override the normal order of things? Do hooks that are created with a node_invoke go before or after the hooks created with module_invoke_all within the same module?

In other words what is the purpose of node_hook ? Can I use it to set a hook private to a module so that other than the ones I set?

An example would be could I set up and use node_invoke in a paypal module to create hooks so that only paypal framework module can see them?