This library is historically used by the Apache Maven project so it's developed and maintained by the same bad guys
The current master is now at https://github.com/codehaus-plexus/plexus-utils
For publishing the site do the following:
mvn -Preporting verify site site:stage scm-publish:publish-scm
Starting with version 4, XML classes (in org.codehaus.plexus.util.xml and org.codehaus.plexus.util.xml.pull) have been extracted to a separate plexus-xml library: if you need them, just use this new artifact.
plexus-utils 4 keeps an optional dependency on plexus-xml 3 to keep compatibility with the few XML-oriented methods of ReaderFactory and WriterFactory: these classes are deprecated, you should migrate as explained in javadoc. And keep plexus-xml to 3 if you want Maven 3 compatibility, as plexus-xml 4 works only in Maven 4.