If the error is not caught, the polling doesn't early exit and can lead
to unexpected time outs with no context or errors on what went wrong.

XPath and evaluate are not available on DocumentFragments. This change
adds a function to allow the DocumentFragment to be converted into a
document and then be able to run the XPath evaluate against it.

When a DocumentFragment is found in XPathQueryEngine, convert it to a
document first before running evaluate with XPath against it. evaluate
and XPath do not work on DocumentFragments.