confusing messages about `type` from xmllint when trying RELAX NG pattern facet

Question

I'm still learning RELAX NG, and some input requires me to check the data content with a pattern. After searching the web I tried this (fragment, modeled after the example in The Simplest Possible Pattern Facets):

  <define name="DT.Test">
    <a:documentation>Data Type: test</a:documentation>
    <data type="string">
      <param name="pattern">"[0-9]+"</param>
    </data>
  </define>

However when running xmllint using that, I got an error message saying:

element data: Relax-NG parser error : Type library 'http://relaxng.org/ns/structure/1.0' does not allow type parameters

So I removed the type parameter and tried again with this definition:

  <define name="DT.Test">
    <a:documentation>Data Type: test</a:documentation>
    <data>
      <param name="pattern">"[0-9]+"</param>
    </data>
  </define>

Astonishingly the message was:

element data: Relax-NG parser error : data has no type

So it seems xmllint is unhappy with both: Specifying a typeattribute, and not specifying one. I'm confused.

Appendix

Version of xmllint

> xmllint --version
xmllint: using libxml version 20904
   compiled with: Threads Tree Output Push Reader Patterns Writer SAXv1 FTP HTTP DTDValid HTML Legacy C14N Catalog XPath XPointer XInclude Iconv ISO8859X Unicode Regexps Automata Expr Schemas Schematron Modules Debug Zlib Lzma

Answer 1

Still I don't quite understand the messages, but adding a datatypeLibrary attribute to the data element makes xmllint happy:

  <define name="DT.Test">
    <a:documentation>Data Type: Test</a:documentation>
    <data datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
          type="string">
      <param name="pattern">"[0-9]+"</param>
    </data>
  </define>