PIDF - schema, making basic optional

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:cpim-presence:"
xmlns:tns="urn:ietf:params:cpim-presence:"
xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified"
attributeFormDefault="unqualified">

   <xs:element name="presence" type="tns:presence"/>
   
   <xs:complexType name="presence">
      <xs:sequence>
         <xs:element name="tuple" type="tns:tuple" maxOccurs="unbounded"/>
         <xs:element name="note" type="xs:string" minOccurs="0"
maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="entity" type="xs:anyURI" use="required"/>
   </xs:complexType>
   
   <xs:complexType name="tuple">
      <xs:sequence>
         <xs:element name="status" type="tns:status"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
         <xs:element name="contact" type="tns:contact" minOccurs="0"/>
         <xs:element name="note" type="xs:string" minOccurs="0"
maxOccurs="unbounded"/>
         <xs:element name="timestamp" type="xs:dateTime" minOccurs="0"/>
      </xs:sequence>
      <xs:attribute name="id" type="xs:ID" use="required"/>
   </xs:complexType>
   
   <xs:complexType name="status">
      <xs:sequence>
         <xs:element name="basic" type="tns:basic" minOccurs="0"/>
         <xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
      </xs:sequence>
   </xs:complexType>
   
   <xs:simpleType name="basic">
      <xs:restriction base="xs:string">
         <xs:enumeration value="open"/>
         <xs:enumeration value="closed"/>
      </xs:restriction>
   </xs:simpleType>
   
   <xs:complexType name="contact">
      <xs:simpleContent>
         <xs:extension base="xs:anyURI">
            <xs:attribute name="priority" type="xs:unsignedByte"/>
         </xs:extension>
      </xs:simpleContent>
   </xs:complexType>
   
   <!-- Global Attributes -->
   <xs:attribute name="mustUnderstand" type="xs:boolean" default="0"/>
</xs:schema>


  [reminder: [email protected] for non-technical discussions, please]