VXML2.0 question pertaining to timing and scoping of error.semantic on bad property names

I can't figure out if the VXML2.0 spec specifies the scope at which
the error.semantic
for a bad property name is thrown.  Is a bad property name a parsing
error that will foul
the document so that the error would be thrown in the referring
context, like a badfetch
on a goto next, or is a bad property name an execute-time error that
may be handled
by a catch elt that is sibling to the offending property elt, the
throwing of it deferred until
the elt in question is initialized (for a dialog) or executed (for a form item)?

-- 
He thought he could organize freedom
how naive and controlling of him