This issue was identified by Matthias Trapp in the Red Hat Customer Discussion forum.

There are various examples for jboss-all.xml in the docs where 'umlns' is a typo for 'xmlns'. For example: https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.0/html/configuration_guide/deploying_applications#control_order_deployments

I have confirmed with bstansbe@redhat.com that despite it appearing in various upstream examples and test cases, this is indeed a typo. He has opened WFLY-10921 to fix the upstream occurrences.

Why this typo hasn't caused a lot of issues despite its longevity:

A document with this typo will fall under the 'no xmlns' category. The parser ignores other attributes on the element, which is why the typo doesn't cause problems.