@when('config.changed')

[Nick Moffitt]

Cory Johns:
> If a charm config option has changed, the state "config.changed" will
> be set for the duration of the hook.  Additionally, specific states
> will be set for each config option that changed; that is, if option
> "foo" has changed, the state "config.changed.foo" will be set.  

Ah, this is perfectly natural syntax, and I have been wishing for
something along this line for a while!

Could we do something similar for relation values, or is the namespace
just too complicated with all the dimensions it affords?

-- 
Nick Moffitt