I was experimenting with something on the just released WildFly 11 and lazily added the "system-properties" element within the server element, after the socket-binding-group in standalone.xml. Something like this: <server xmlns="urn:jboss:domain:5.0">     .....     <socket-binding-group>     ...     ....     </socket-binding-group>     <system-properties>         <property name="test.wfly" value="hello world"/>     </system-properties> </server> Then booted the standalone server and ran into this improved error message at startup: 17:51:32,950 ERROR [org.jboss.as.controller] (Controller Boot Thread) OPVDX001: Validation error in standalone.xml ----------------------------------- | |  510:     </socket-binding-group> |  511: |  512: *<system-properties>** **|           ^^^^ 'system-properties' isn't an allowed element here* | | *Elements allowed here are: * |                  deployment-overlays   management *system-properties* |                  deployments           paths vault |                  extensions            profile |                  interfaces            socket-binding-group | |  513:         <property name="test.wfly" value="hello world"/> |  514:     </system-properties> |  515: | | 'system-properties' is allowed in elements: | - server | " | | The primary underlying error message was: | > ParseError at [row,col]:[512,5] | > Message: WFLYCTL0198: Unexpected element | >   '{urn:jboss:domain:5.0}system-properties' encountered | I understand why it errored out (it expects the system-properties to be after the "extensions" element, than at the end) and I fixed the config to get past it. However, the interesting bit is that the error message that it threw states that "system-properties" isn't allowed at that location and the elements that are allowed there displays a bunch of elements which also includes "system-properties". I haven't looked up the code to see how that log message is generated and if it's just a logging issue or something more. Thought of noting it here in the list. -Jaikiran