clarified double role of id property

git-svn-id: https://src.springframework.org/svn/spring-framework/trunk@2524 50f2f4bb-b051-0410-bef5-90022cba6387

org.springframework.context/src/main/resources/org/springframework/scheduling/config/spring-task-3.0.xsd

@@ -84,7 +84,10 @@
 				<xsd:annotation>
 					<xsd:documentation><![CDATA[
 	The bean name for the generated ThreadPoolTaskExecutor instance.
-	It will also be used as the default thread name prefix.
+	This value will also be used as the thread name prefix which is why it is
+	required even when defining the executor as an inner bean: The executor
+	won't be directly accessible then but will nevertheless use the specified
+	id as the thread name prefix of the threads that it manages.
 					]]></xsd:documentation>
 				</xsd:annotation>
 			</xsd:attribute>