Section 12.1 (which should be satisfied in SE an EE) states:

An implicit bean archive is any other archive which contains one or more bean classes with a bean defining annotation as defined in Bean defining annotations.

And section 15.1 reads:

When running in Java SE, the container must extend the rules defined in Bean archives and also ensure that :
An archive which doesn’t contain a beans.xml file can’t be discovered as an implicit bean archive unless:

• the application is launched with system property javax.enterprise.inject.scan.implicit set to true, or
• the container was initialized with a parameter map containing an entry with javax.enterprise.inject.scan.implicit as key and Boolean.TRUE as value.

Perhaps this deserve a bit of clarification.