Passing properties into a FlowCallout

[#1]

The FlowCallout policy appears to support the ability to pass properties into the shared flow. Can anyone provide an example of how to do this?

The policy XML I have looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<FlowCallout async="false" continueOnError="false" enabled="true" name="FC-Fault-Handling-Default-v1">
  <DisplayName>FC-Fault-Handling-Default-v1</DisplayName>
  <FaultRules/>
  <Properties>
  </Properties>
  <SharedFlowBundle>fault-handling-default-v1</SharedFlowBundle>
</FlowCallout>

How do I use the properties tag? The documentation doesn't mention this tag.

thanks