Questions about DOM 1.0

Reading the DOM 1.0 recommendation leads to the follwing questions:

- Interface NamedNodeMap, Method removeNamedItem
  DOM says: 
    Return Value: The node removed from the map or NULL if no node with
such a name exists.
    Exceptions: NOT_FOUND_ERR: Raised if there is no node named 'name' in
the map

  If you throw an exception, why return something at all?

- Interface Node, Attribute nodeValue
  DOM says:
    Exceptions on setting: NO_MODIFICATION_ALLOWED_ERR: raised when the
node is readonly.

  Certain nodes (ie Document) does not have any nodeValue at all (NULL).
What will happen if someone tries to set the nodeValue on such a node? What
does "readonly" mean?

Holger Floerke