Change definitons of explicit/implicit archive, add notion about back…

…wards compatibility.

spec/src/main/asciidoc/core/packagingdeployment.asciidoc

@@ -32,10 +32,12 @@ is not a bean archive.
 An _explicit bean archive_ is an archive which contains a `beans.xml` file:
 
 * with a version number of `1.1` (or later), with the `bean-discovery-mode` of `all`, or,
-* with no version number, or,
-* that is an empty file.
+* with no version number.
 
-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>>.
+An _implicit bean archive_ is:
+
+* an archive which contains a `beans.xml` file that is empty, or,
+* any other archive which contains one or more bean classes with a bean defining annotation as defined in <<bean_defining_annotations>>.
 
 When determining which archives are bean archives, the container must consider:
 
@@ -48,6 +50,8 @@ The `beans.xml` file must be named:
 
 * `META-INF/beans.xml`.
 
+For compatibility with CDI versions prior to 4.0, {cdi_full} products must contain an option that causes an archive with empty beans.xml to be considered an explicit bean archive.
+
 The container searches for beans in all bean archives in the application classpath.
 
 If a bean class is deployed in two different bean archives, non-portable behavior results.