Similar to a CurrentNodeListIterator except that the filter has a
simpler interface (only needs the node, no position, last, etc.)
It takes a source iterator and a Filter object and returns nodes
from the source after filtering them by calling filter.test(node).
This class is duplicated for each JAXP subpackage so keep it in sync.
It is package private and therefore is not exposed as part of the JAXP
API.
This code is designed to implement the JAXP 1.1 spec pluggability
feature and is designed to run on JDK version 1.1 and
later, and to compile on JDK 1.2 and onward.