Using Schema XDOC 2.0
The XDOC XSD is located here.
Your favorite IDE probably supports XSD schema's for .xml/.xdoc files. You need to specify the following:
<document xmlns="http://maven.apache.org/XDOC/2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 https://maven.apache.org/xsd/xdoc-2.0.xsd"> ... </document>