DocBook Publisher - stagedir

I'm using the following to Xinclude several plays into one larger document, with OxygenXML 18. 

<?xml version="1.0" encoding="UTF-8"?>

<?xml-model href="" href="http://docbook.org/xml/publishers/5.1CR3/publishers.rng">http://docbook.org/xml/publishers/5.1CR3/publishers.rng" schematypens="http://relaxng.org/ns/structure/1.0" ?>

<part xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" remap="Play">

However, the stagedir and inlinestagedir elements do not validate.

I am using <para remap="stagedir"> as a work around.

Changing the <book/> to 

<part xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0" remap="PLAY"> 

was easy - all other elements remained the same, and prefaces, etc., stay as they are.

With thanks Paul