At this point in time only 3 of the several operation handlers available to create custom workflows are documented. Furthermore having documentation detailing the inner workings of each of the operation handlers is essential to troubleshoot workflows failures.
Ideally they would be an Operation Handler Documentation Template used for all of them. This template is most likely to be better outlined by a Java Developer that understands the operation handlers, however here is some ideas for such template:
-inputs (data structure, options)
-outputs (data structures)
-Rest calls (internal to the MH cluster, external, internal to the operation handler itself which would be equivalent to the REST docs)
-Relationship with flavors
-Services/other operations handlers dependencies
Once this template is in place a new operation handler should not be accepted without such documentation. The documentation pages should also be permanent so they can be referred within log statement or configuration files.