1 if vrnode object is valid, 0 if not
x = isvalid(vrnode_object_vector)
This method returns an array that contains 1 when the elements of vrnode_object_vector are valid vrnode objects, and 0 when they are not.
The vrnode object is considered valid if the following conditions are met:
The parent world of the node exists.
The parent world of the node is open.
The VRML node with the given vrnode handle exists in the parent world.