<xsd:complexType name="TregistrationListener">
 <xsd:annotation>
 <xsd:documentation>
 <![CDATA[
 A registration listener definition. The target registration listener
 can be either a <ref> to a <bean> or <service> component, or an inline
 <bean> or <service> component definition. The registration-method and
 unregistration-method attributes define the methods that will be called
 for the respective events.

 For the very common case of using a <ref> to a listener component, the
 ref attribute may also be used as a shortcut.
 ]]>
 </xsd:documentation>
 </xsd:annotation>
 <xsd:group ref="targetComponent" />
 <xsd:attribute name="ref" type="Tidref" use="optional" />
 <!-- ### why are there both required? -->
 <xsd:attribute name="registration-method" type="Tmethod" use="required" />
 <xsd:attribute name="unregistration-method" type="Tmethod" use="required" />
 </xsd:complexType>

 <xsd:group name="targetComponent">
 <xsd:annotation>
 <xsd:documentation>
 <![CDATA[
 A targetcomponent is one that can be a target for a
 listener, registration-listener, or type-converter element.
 This is used in contexts where the requirement is a single
 provided object that will implement a particular interface.
 The provided object is obtained either from a <ref> element
 or inline (<bean> or <reference>).
 ]]>
 </xsd:documentation>
 </xsd:annotation>
 <xsd:choice>
 <xsd:element name="bean" type="Tbean" />
 <xsd:element name="reference" type="Treference" />
 <xsd:element name="ref" type="Tref" />
 <xsd:any namespace="##other" processContents="strict" minOccurs="0" maxOccurs="unbounded" />
 </xsd:choice>
 </xsd:group>

Associated JIRA

https://jira.jboss.org/jira/browse/JBXB-211

you might be pleased to hear that I successfully moved BP parsing to XB annotations ;-)