InstanceDataField 

Used to store the instance id of the subflow instantiated by the activity. This is then available later on (e.g. for correlation, messaging etc.) especially in the case of asynchronous invocation.

Attribute Information

Used By

Element xpdl:SubFlow

Source 

<xsd:attribute name="InstanceDataField" type="xsd:string" use="optional">
  <xsd:annotation>
    <xsd:documentation>Used to store the instance id of the subflow instantiated by the activity. This is then available later on (e.g. for correlation, messaging etc.) especially in the case of asynchronous invocation.</xsd:documentation>
  </xsd:annotation>
</xsd:attribute>

Sample