If you are ever called upon to diagnose or repair network connectivity issues, you know that the first thing to check is the network cable.
Well, much to my chagrin, there is a similar principle to follow when debugging XQuery statements.
If you type an element name incorrectly, you may not get an error from the query and it will happily complete, sans your expected content.
To broaden that a bit, the first thing to check, outside of reported syntax and type errors, are your XPath expressions, including the spelling of element names.
Especially for no errors but also not the expected result cases.
Thus ends the XQuery lesson for the day.