ched.  Derived classes that implement iterators
 must override runTo(int index), in order that they may
 run the iteration to the given index. </p>
 
 <p>Note that we directly implement the DOM's NodeIterator
 interface. We do not emulate all the behavior of the
 standard NodeIterator. In particular, we do not guarantee
 to present a "live view" of the document ... but in XSLT,
 the source document should never be mutated, so this should
 never be an issue.</p>
 
 <p>Thought: Should NodeSet really implement