onopen

When the service comes up it triggers a notify or solicit referenced by relative path. The referenced operation must have the service as its client and a JSON field named event.

<folder name="Folder">
  <service name="Expr" 
    provision="expr">
    <prop name="instance.spec" 
      onopen="Mix/OnOpen"/>
  </service>
  <mix name="Mix">
    <field name="event" 
      type="json"/>
    <notify name="OnOpen" 
      service="Sequencer" 
      clients="Expr" 
      fields="event"/>
  </mix>
</folder>