As https://issues.jenkins-ci.org/browse/JENKINS-38864 is likely to be a bit of rocket science, there is still a need to allow users to document their pipelines in a model friendly way, that the blue ocean editor (for example) can read, and allow users to edit. 

The comments may also be useful for people diagnosing broken steps etc

If there was a way to annotate or have a meta data field for parts of the pipeline declarative model, this could be really helpful. 

In terms of syntax, I don't have concrete ideas - it could be an attribute, an annotation, or someting. Anything really.