Please describe the problem:
I found a case where a document that both the "Jing" relaxng validator and the "relames" validator deem valid, is not validated by libxml2's RelaxNG validation.  

Included in this report are a minimal rng schema and a minimal document that exposes the problem.

Steps to reproduce:
schema.rng:

<element name="root" xmlns="http://relaxng.org/ns/structure/1.0">
  <choice>
    <element name="child">
      <attribute name="type">
        <value>Foo</value>
      </attribute>
      <!-- Define stuff that's only valid when type is "Foo" -->
    </element>
    <element name="child">
      <attribute name="type">
        <value>Bar</value>
      </attribute>
      <!-- Define stuff that's only valid when type is "Bar" -->
    </element>
  </choice>
</element>

document.xml:

<root>
  <child type="Foo">
  </child>
</root>

$ xmllint --relaxng schema.rng document.xml


Actual results:
xmllint output:

<?xml version="1.0"?>
<root>
  <child type="Foo">
  </child>
</root>
document.xml:2: element child: Relax-NG validity error : Element child failed to validate attributes
document.xml fails to validate


Expected results:
relames output:

relmes verifier   Copyright(C) Sun Microsystems, Inc. 2001
parsing    schema.rng
validating document.xml
valid




Does this happen every time?
yes

Other information:
Although I did see other bug reports about incorrect validation behaviour, I think this is another individual case. I hope this report is helpful.