Have a section in the user guide on the general task and tasklist concept; this should cover task state (i.e. what is an assignee, a candidate user, ...?), lifecycle, and Java API how to change state and trigger lifecycle transitions (similar to what we created for external tasks recently).
The lifecycle could be central to the explanations. Judging from the feedback on the CMMN docs, I have the feeling that people are able to understand lifecycle diagrams.
Have sections in "Webapps => Tasklist", BPMN Reference, and CMMN Reference that describe how the model-language- or UI-specific concepts map to the abstract task concept. Have bi-directional links between the sections.
Task
L3 - Default