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CMMN differentiates between plan items and plan item definitions. While plan items represent actual units of work that are enacted as part of the case, plan item definitions serve as the blueprint for how a plan item has to be enacted. This concept simplifies reuse of plan item definitions and furthermore enables dynamic planning so that additional items can be generated from a definition at runtime. As an example, consider the following fragment of a case definition: 
<definitions>
  <case id="case" name="Case">
    <casePlanModel id="CasePlanModel_1">
      <planItem id="PlanItem_HumanTask_1" definitionRef="HumanTask_1" />
      <planItem id="PlanItem_HumanTask_2" definitionRef="HumanTask_1" />

      <humanTask id="HumanTask_1" camunda:assignee="kermit" />
    </casePlanModel>
  </case>
</defintions>
This model contains one plan item definition, namely the humanTask element. This definition is referenced by two plan items, PlanItem_HumanTask_1 and PlanItem_HumanTask_2. When a new case of this model is created, there will be two human task instances, one for each plan item. The plan item definition is the single point at which the human task is configured. Thus, the assignee specification by the attribute camunda:assignee="kermit" is valid for both plan items. Accordingly, a case plan model that contains plan item definitions but no plan items will appear as a case with no tasks at runtime. Apart from reuse of configuration, plan item definitions can be instantiated at runtime, typically referred to as planning. Planning allows users to create plan items of a well-defined set of plan item definitions dynamically as needed. Note that planning is currently not supported by the ASEE Flow engine. This reference describes, if not otherwise noted, the plan item definitions supported by the ASEE Flow engine. Whenever there is a consideration of runtime state, it is assumed that a plan item referencing that definition exists.