REST Task is documented here:
https://access.redhat.com/documentation/en-us/red_hat_jboss_bpm_suite/6.4/html/user_guide/appe_service_tasks#rest_task

One of the possible input attribute is called ContentType.

Currently, it makes sense to use only these two values for ContentType:

• application/xml
• application/json

See source for more details https://github.com/kiegroup/jbpm/blob/6.5.x/jbpm-workitems/src/main/java/org/jbpm/process/workitem/rest/RESTWorkItemHandler.java#L339-L343

Please mention these two values explicitly in the docs.

This issue applies to both, BPM Suite 6 and RHBA 7.