style

<xs:attribute name="style" default="single">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="single"/>
      <xs:enumeration value="double"/>
      <xs:enumeration value="dash"/>
      <xs:enumeration value="dots"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>