I have some text in a node, for example:

<?xml version='1.0' encoding='utf-8'?>
<xml><Hello world "&" foo bar></xml>

I would like to process /xml/string() and output:

"<Hello world "&" foo bar>"

How can I do it with XPath 3.1?

REMARK: The question is more general than just JSON-escaping the " in the example.