(1) describes that one should use the structs-plugin to add @Symbol to an extension point, but at (2) an other approach is described: one should use org.jenkins-ci:symbol-annotation. Which is correct? What are the benefits of one over the other? Why should I use (1) instead of (2)?

(1) https://wiki.jenkins-ci.org/display/JENKINS/Structs+plugin
(2) https://github.com/jenkinsci/pipeline-plugin/blob/master/DEVGUIDE.md#defining-symbols