Javadoc
Fetch DOM node / JAXB object pairs matching an XPath (for example "//w:p").
In JAXB, this association is partial; not all XML elements have associated JAXB objects,
and not all JAXB objects have associated XML elements.
If the XPath returns an element which isn't associated
with a JAXB object, the element's pair will be null.
If you have modified your JAXB objects (eg added or changed a
w:p paragraph), you need to update the association. The problem
is that this can only be done ONCE, owing to a bug in JAXB:
see https://jaxb.dev.java.net/issues/show_bug.cgi?id=459
So this is left for you to choose to do via the refreshXmlFirst parameter.