Take the following method call defining an attribute: -

.setCapabilityReference(PROVIDERS_CAPABILITY, SASL_SERVER_FACTORY_CAPABILITY, true)

This definition says this attribute references something which provides the PROVIDERS_CAPABILITY.

However it also states that the resource that contains this attributes provides the SASL_SERVER_FACTORY_CAPABILITY.

Really what the resource provides is not directly related to this attribute definition.

The following pull request has already improved on registering in advance what capability a resource can provide: -

https://github.com/wildfly/wildfly-core/pull/909