Note: This also dumps the tag that defines the node you are trying to dump. It is useful because it is the only way I could find to get a node's content including the tags in it.
From this xml bit of file:
Blah blah blah <some_stuff/>
doing a dump_node on this block node will return exactly all of the xml typed above, including the <block> tags. Trying to get the value or content of the node, however, will only return "Blah blah blah" as <some_stuff> is considered a child, not part of the /text() xpath.