Hi current there is no way you can't a parse an XML-DOM document wihout knowing the real structure of the XML in advance, or either we cannot get the full content of a node (including other inner tags) with ExtractValue,

They are limited only to node value. so it is needed that thos functions can suppor more XPath 1.0 conventions to make this possible.
Ref: XPath 1.0 Specificacion

Or implement additional functions to manipulatean XMl document. Like JSON functions.
Here is a link for an UDF that can help:

https://www.codeproject.com/Articles/71336/MySQL-XML-User-Defined-Functions