Plugins that can record several results in the same build (like the coverage plugin, which can report a code coverage and a mutation coverage result) use an ID to distinguish these results. This ID is exposed as the URL name of the corresponding action.
With this parameter you can restrict the search for a reference build to those builds that provide an action with the given ID. All builds that do not provide such an action will be skipped, and the search continues with the predecessors of these builds.
This parameter can be combined with the required action type: then the reference build must provide an action that matches both the type and the ID. If the type is left empty, then the ID alone is used to select the matching action. If this parameter is left empty, then the ID of the action is not relevant.