Strange construction in XForms schema

Hi all,

I'm a bit confused by the XForms schema.

The selectOne element is defined as follow:

  <xsd:element name="selectOne">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:group ref="xform:commonUIChildren"/>
        <xsd:element ref="xform:choices"/>
      </xsd:sequence>
      <xsd:attribute name="id" type="xsd:ID" use="optional"/>
      <xsd:attributeGroup ref="xform:bindFirstAttributes"/>
      <xsd:attributeGroup ref="xform:commonUIAttributes"/>
      <xsd:attribute name="selectUI" type="xform:selectUIType"
use="optional"/>
    </xsd:complexType>
  </xsd:element>

The definition of commonUIChildren is:

  <xsd:group name="commonUIChildren">
    <xsd:all>
      <xsd:element ref="xform:caption"/>
      <xsd:element ref="xform:help" minOccurs="0"/>
      <xsd:element ref="xform:hint" minOccurs="0"/>
      <xsd:element ref="xform:alert" minOccurs="0"/>
      <xsd:element ref="xform:action" minOccurs="0"/>
      <xsd:element ref="xform:extension" minOccurs="0"/>
    </xsd:all>
  </xsd:group>


So the final model is:

<sequence>
    <all>
        ...
    </all>
     ...
</sequence>

According to Schema Structure 3.8.2, this seems to be an invalid construct.

Since I'm far from being a Schema guru, I'd really appreciate opinions from
the list.

Thanks,

Jérôme Nègre