I suspect this is a defect in the documentation for this handler.
Elsewhere in the doc you will see definitions similar to the following;
Builds a list of all users who are reviewers in the same task level as the current reviewer and sends e-mail to all of them.
Sends e-mail to all members assigned as the proposed reviewers of the first target object in the workflow process.
Sends e-mail to the designated responsible party for the task.
Sends e-mail to the member assigned as the proposed responsible party of the first target object in the workflow process.
PROPOSED_REVIEWERS and PROPOSED_RESPONSIBLE_PARTY are keywords that map to a dynamic participant on the workflow target. You can see the definition of the participants in BMIDE.
RESPONSIBLE_PARTY is the current responsible party for the task.
REVIEWERS is derived from the signoffs for the task.
Good afternoon, thanks for the answer.
This is used only for the Change Management object? As far as I know, only these objects are assigned dynamic participants
It's possible to define your own dynamic participants in BMIDE and specify to which objects they apply (though it must be a subtype of ItemRevision). When you define the participant type you can specify the keyword you wish to use in workflow handlers, and if it should be a single assignee, or multiple.
Having said that some of the handlers do have keywords that are documented as specific to change objects.