title: Is it possible to include a docbook "article" into a "book"?
body: <p>got a problem with the generation from docbook to PDF. </p>
  
  <p>I need to generate one PDF based on several docbook-xmls. Some of these XMLs are manually written (as the shown excerpt "book.xml" below), some of the are generated by OxygenXML (second excerpt below). The latter are XSD-schemata transferred into docbook using OxygenXML. As Oxygen does not have an option here, it always produced a docbook "article". </p>
  
  <p>The file that include these articles is a docbook "book". However, inclusion produces errors: first error tells that:</p>
  
  <pre><code>element "article" from namespace "http://docbook.org/ns/docbook" 
  not allowed in this context
  </code></pre>
  
  <p>my book.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;book version="5.1" xml:lang="en" xmlns="http://docbook.org/ns/docbook"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xlink2="http://www.w3.org/1999/xlink"
    xmlns:xlink="http://www.w3.org/1999/xhtml"
    xmlns:xi="http://www.w3.org/2001/XInclude"
    xmlns:ns6="http://www.w3.org/2000/svg"
    xmlns:ns5="http://www.w3.org/1998/Math/MathML"
    xmlns:ns2="http://docbook.org/ns/transclusion"
    xmlns:ns="http://docbook.org/ns/docbook"&gt;
  
  &lt;title&gt;xyz&lt;/title&gt;
  
  &lt;chapter&gt;
    &lt;title&gt;my xsd previously rendered by oxygen&lt;/title&gt;
    &lt;xi:include href="generated_schemata/my_xsd.xml"/&gt;
  &lt;/chapter&gt;
  ...
  </code></pre>
  
  <p>and the beginning of the generated my_xsd.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;?oxygen RNGSchema="http://www.oasis-open.org/docbook/xml/5.0/rng/docbook.rng" type="xml"?&gt;
  &lt;!--XML Schema documentation generated by &lt;oXygen/&gt; XML Developer.--&gt;
  &lt;article version="5.0" xmlns="http://docbook.org/ns/docbook"
       xmlns:ns5="http://www.w3.org/1998/Math/MathML"
       xmlns:ns4="http://www.w3.org/1999/xhtml"
       xmlns:ns3="http://www.w3.org/2000/svg"
       xmlns:ns2="http://www.w3.org/1999/xlink"
       xmlns:ns="http://docbook.org/ns/docbook"&gt;
    &lt;title&gt;Schema documentation for ServiceCatalogue.xsd&lt;/title&gt;
  
    &lt;info&gt;
      &lt;pubdate&gt;february 20, 2018&lt;/pubdate&gt;
    &lt;/info&gt;
  
    &lt;section&gt;
      &lt;title&gt;Namespace: ""&lt;/title&gt;
  ...
  </code></pre>
  
  <p>Question: is there any way to include an docbook "article" into a "book" (or some other structure, so in the end, I get one PDF)?</p>
  
  <p>Tools I am using are maven together with docbkx-plugin.</p>