readonly and setvalue

As per section 6.1.2

"When evaluating to true, this model item property indicates that the
XForms Processor should not allow any changes to the bound instance data
node"

Am I reading the spec correct
1. "calculate" is also readonly for the "user" 
2. "readonly" is for the model

So what should happen if a "<setvalue>" attempted on a readonly node?
Should an Exception/error be dispatched?


Regards