The online reference documentation for the Jenkins Pipeline checkout step is automatically extracted from released plugin online help pages.
Several of the fields in the GitSCM online documentation include no description. The following fields are examples of fields that should be described so that readers know how to use them:
Add help for those fields by following the same naming convention and file placement elsewhere in the plugin. The help files are html files placed in the src/resources directory. See the references option as an example.