Document that @Async is not supported in @Configuration classes

spring-context/src/main/java/org/springframework/scheduling/annotation/Async.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,9 @@ import java.lang.annotation.Target;
 /**
  * Annotation that marks a method as a candidate for <i>asynchronous</i> execution.
  * Can also be used at the type level, in which case all of the type's methods are
- * considered as asynchronous.
+ * considered as asynchronous. Note, however, that {@code @Async} is not supported
+ * on methods declared within a
+ * {@link org.springframework.context.annotation.Configuration @Configuration} class.
  *
  * <p>In terms of target method signatures, any parameter types are supported.
  * However, the return type is constrained to either {@code void} or
@@ -55,13 +57,13 @@ public @interface Async {
 
 	/**
 	 * A qualifier value for the specified asynchronous operation(s).
-	 * <p>May be used to determine the target executor to be used when executing this
-	 * method, matching the qualifier value (or the bean name) of a specific
-	 * {@link java.util.concurrent.Executor Executor} or
+	 * <p>May be used to determine the target executor to be used when executing
+	 * the asynchronous operation(s), matching the qualifier value (or the bean
+	 * name) of a specific {@link java.util.concurrent.Executor Executor} or
 	 * {@link org.springframework.core.task.TaskExecutor TaskExecutor}
 	 * bean definition.
-	 * <p>When specified on a class level {@code @Async} annotation, indicates that the
-	 * given executor should be used for all methods within the class. Method level use
+	 * <p>When specified on a class-level {@code @Async} annotation, indicates that the
+	 * given executor should be used for all methods within the class. Method-level use
 	 * of {@code Async#value} always overrides any value set at the class level.
 	 * @since 3.1.2
 	 */