https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html-single/configuration_guide/index#microprofile_config_supported_configsources in the "Obtaining ConfigSource Configuraton from a ConfigSource Class"[1] section and the "Obtaining ConfigSource Configuraton from a ConfigSourceProvider Class"[2] section both include this paragraph:

"For information about how to add a global module to the JBoss EAP server, see Define Global Modules."

That links to https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html-single/configuration_guide/index#add_a_global_module.

Problem is the content in that section is not related to adding custom module that's referenced by container resources configured in standalone/host/domain.xml. That section is about how to tell the the server to make a particular module available to all deployments which is a different thing.

https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html-single/configuration_guide/index#create_a_custom_module is the appropriate thing to link to, e.g.

"For information about how to add a custom module to the JBoss EAP server, see Create a Custom Module."

[1] Note there's a typo in that section heading
[2] Same typo

jmesnil1@redhat.com yborgess1@redhat.com FYI.