Polish CorsFilter Javadoc

spring-web/src/main/java/org/springframework/web/filter/CorsFilter.java

@@ -38,6 +38,11 @@ import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
  * {@link CorsConfigurationSource} (for example an {@link UrlBasedCorsConfigurationSource}
  * instance.
  *
+ * <p>This is an alternative to Spring MVC Java config and XML namespace CORS configuration,
+ * useful for applications depending only on spring-web (not on spring-webmvc) or for
+ * security constraints requiring CORS checks to be performed at {@link javax.servlet.Filter}
+ * level.
+ *
  * <p>This filter could be used in conjunction with {@link DelegatingFilterProxy} in order
  * to help with its initialization.
  *