pipe below fails in Calabash .9

<?xml version="1.0"?> <p:declare-step xmlns:p="http://www.w3.org/ns/xproc"> <p:input port="source" primary='true'> <p:document href="doc.xml"/> </p:input> <p:output port='result'> <p:document href="op.xml"/> </p:output> <p:identity/> </p:declare-step>

I want to define a pipe with both input and output files specified by the pipe.

http://www.w3.org/TR/xproc/#c.xslt seems to specify both, I'm unsure why mine doesn't work?

Error : file:/files/xproc/tests/pipe3.xpl:2: Unbound primary output port on last step: #ANON.85 Error : Pipeline failed: com.xmlcalabash.core.XProcException: Don't know how to handle binding 3

Any suggestions where / why I'm wrong please?