Utility methods on DOM elements for key/keyref/unique

Hello,

For Xopus I am building support for the key, keyref and unique
declarations, and I was wondering if there are DOM methods defined
somewhere that allows a programmer to use this extra structure in an XML
document.

I have found the XML Schema API, which is great for validation, but not
for anything more.

I was thinking of at least two methods:

Element.getElementByKey(String keyName, 
  Object fieldValue [, Object fieldValue]*): Element
Works on instances of elements which have a declaration with a "key" or
"unique" ID constraint with the name keyName.
Returns the element that has the fieldValue(s) as key sequence or null
otherwise.

Element.resolveKeyReference(String keyName): Element
Works on elements which are matched by a selector of the "keyref"
declaration with the name keyName.
Returns the element that matches the key sequence of the key reference.

Does anyone know of such or similar methods? If not, would such methods
be useful? (I have never worked with XML documents with key/keyrefs
myself.) Are there any other methods that could be useful?

Greetings,

Sjoerd Visscher
Xopus: http://xopus.com
+31 (0)70 - 3699563
http://maps.google.com/?q=xopus+den+haag+nederland&z=18&t=h