Child inherit.append.path attributes not defined in Maven POM XSD

The child inherit.append.path attributes, introduced in Maven 3.6.0, are not defined in the Maven POM XML Schema Definition: http://maven.apache.org/xsd/maven-4.0.0.xsd

This is causing XML Validators to report the following error: cvc-complex-type.3.2.2: Attribute 'child.site.url.inherit.append.path' is not allowed to appear in element 'site'.

The error is for instance visible in Eclipse POM editor or while attempting to deploy artifacts to Maven Central, as they validate project POMs against maven-4.0.0.xsd.