Dom level 3 xpath variable support

After complaining on xml-dev on the badly documented facilities
available in XPath processors for variable binding, could I urge the
working group to please add proper support for variable binding to DOM
level 3?

For example,

interface XPathVariableContext {
   XPathResult resolve(in DOMString name);
}

interface XPathEvaluator {
   ....
   void setContext(int XPathVariableContext context);
}

a simple change.. without which writing applications that depend on
passing variables to xpath processors are a nightmare to write. 

Thanks,
Christian Nentwich