NavState vs. Interaction State or what is the purpose of interactionstate?

[Michael Freedman <michael.freedman@oracle.com>]

Given the current state of the spec, I am trying to figure out what the 
purpose of interactionState is.  Can anyone help?  My recollection is 
that originally interactionState was the PBI equivalent of 
navigationalState (for getMarkup) prior to us adding the "performance 
enhacement" that passed PBI MarkupParams so action/render response could 
occur in a single request.  This no longer seems to be our intent as 
shown by the URL samples in section 10.2.1.9.  I.e. the second example 
expresses an actionURL with both navigationalState and 
interactionState.  What is the new model?  I can think of something like 
interactionState holds those values that augment the action processing 
while navigationalState holds those values that augment the rendering 
process -- but that seems pretty meaningless given that in most 
applications state is state that you compute with and render from.  I.e. 
why wouldn't developers merely represent all such state as 
NavigationalState (particularly because this form now has an opaque and 
non-opaque portion)?  Since navState doesn't inherently carry forward at 
the end of an action/event, you must explicitly set it it seems to offer 
everything interactionState does but in one object that spans all 
operations.
      -Mike-