anchor.diff:  [[extensions]]
   == Extensions
   
  -Thanks to its great https://kotlinlang.org/docs/reference/java-interop.html[Java interoperability]
  -and to https://kotlinlang.org/docs/reference/extensions.html[Kotlin extensions], Spring
  -Framework Kotlin APIs leverage regular Java APIs and are additionally enhanced by a few Kotlin specific APIs
  -available out of the box within Spring Framework 5 artifacts.
  +Kotlin https://kotlinlang.org/docs/reference/extensions.html[extensions] provide the ability
  +to extend existing classes with additional functionality. The Spring Framework Kotlin APIs make
  +use of these extensions to add new Kotlin specific conveniences to existing Spring APIs.
   
   {doc-root}/spring-framework/docs/{spring-version}/kdoc-api/spring-framework/[Spring Framework KDoc API] lists
   and documents all the Kotlin extensions and DSLs available.
  
positive.code: `@RestController`, `@Service` or `@Repository` are automatically opened since these
  annotations are meta-annotated with `@Component`.
  
  http://start.spring.io/#!language=kotlin[start.spring.io] enables it by default.
  
  === Using immutable class instances for persistence
  
  
negative.code: this specific Kotlin feature can prevent the application from starting, if this fact is not taken in
  consideration. This is because Spring beans are normally proxified with CGLIB
  - such as `@Configuration` classes - which need to be inherited at runtime for technical reasons.
  The workaround was to add an `open` keyword on each class and member
  functions of Spring beans proxified with CGLIB such as `@Configuration` classes, which can
  quickly become painful and is against Kotlin principle to keep code concise and predictable.
  
  Fortunately, Kotlin now provides a
  https://kotlinlang.org/docs/reference/compiler-plugins.html#kotlin-spring-compiler-plugin[`kotlin-spring`]
  plugin, a preconfigured version of `kotlin-allopen` plugin that automatically opens classes
  and their member functions for types annotated or meta-annotated with one of the following
  