subr.spec

Use this property to match a request or consume to a solicit or notify subroutine. The matching is done by specifying the same function for the operations and parameterising the fields. In the case of a solicit-request or solicit-consume/reply pairing, the number and name of the responses have to match the number and name of the replies.

...

<request name="Router1Version" 
  service="ISR" 
  fields="SOME_FIELD">  
  <prop name="subr.spec" 
    function="GetVersion" 
    ancestor="isr4453" 
    Version="router1_version"/>  
  <reply name="Ok" 
    fields="router1_version"/>
</request>   

...

<folder name="isr4453">    
  <solicit name="GetVersion" 
    service="Sequencer"
    clients="Subr"  
    fields="GET_VERSION ISR4453">    
    <prop name="subr.spec" 
      function="GetVersion" 
      Version="version"/>    
    <response name="Ok" 
      fields="version"/>  
  </solicit>

...
Tip: The subr.spec property can also contain Erlang extensions used as predicates.