public static final class Navigator.DescendantEnumeration
General-purpose implementation of the descendant and descendant-or-self axes,
in terms of the child axis.
But it also has the option to return the descendants in reverse document order;
this is used when evaluating the preceding axis. Note that the includeSelf option
should not be used when scanning in reverse order, as the self node will always be
Get another iterator over the same sequence of items, positioned at the
start of the sequence. It must be possible to call this method at any time, whether
none, some, or all of the items in the original iterator have been read. The method
is non-destructive: it does not change the state of the original iterator.