I just get back "<?xml version="1.0" encoding="UTF-8"?>
<ns:error xmlns:ns="http://outerx.org/daisy/1.0"><ns:description>The required
field named "xml" is missing.</ns:description></ns:error>"
(I tried many other ways to write this Post...)
Doc says "Creating a new variant based on an existing variant is rather
different. In this case no XML body or multipart-request must be done, but a
POST operation with the following request parameters:"