The NodeIterator.filter read-only method returns a NodeFilter object, that is an object implement an acceptNode(node) method, used to screen nodes.
The NodeIterator.nextNode() method returns the next node in the set represented by the NodeIterator and advances the position of the iterator within the set.  The first call to nextNode() returns the first node in the set.
The NodeIterator.previousNode() method returns the previous node in the set represented by the NodeIterator and moves the position of the iterator backwards within the set.
The NodeIterator.root read-only property represents the Node that is the root of what the NodeIterator traverses.
The NodeIterator.whatToShow read-only property represents an unsigned integer representing a bitmask signifying what types of nodes should be returned by the NodeIterator.