Valid content model

Dear All,

is the following content model valid ?

It is unambiguous and the "name-type" constraint is fulfilled
is there any other rule that could make it invalid ?

<xsd:element name="X">
  <xsd:complexType>
    <xsd:choice>
        <xsd:element name="A" type="xsd:string"/>
        <xsd:element name="B" type="xsd:string"/>
    <xsd:choice>
    <xsd:element name="C" type="xsd:string"/>
    <xsd:choice>
        <xsd:element name="A" type="xsd:string"/>
        <xsd:element name="B" type="xsd:string"/>
    <xsd:choice>
  </xsd:complexType>
 </xsd:element>

Thank you very much.

Best regards,
Claude.

-- 
______________________________________________

Claude Seyrat

Expway c/o Acland
18 avenue Georges V
75008 Paris
tel: 33 1 56 62 11 06 **new**
fax: 33 1 56 62 11 11
mail: claude.seyrat@expway.tv