XML Schema Either Text Or Sequence

I'd like to assert that the element set either contains a simple
    type or more set elements.

    <set name="phone">
      <set name="type">work</set>
      <set name="number">555-1212</set>
    </set>

    I figured out this bit:

    <xsd:complexType name="set">
      <xsd:simpleContent>
        <xsd:extension type="xs:string">
          <xsd:attribute name="name" type="xs:string"/>
        </xsd:extension>
      </xsd:simpleContent>
    </xsd:complexType>

    I figured out this bit:

    <xsd:complexType name="set">
      <xsd:sequence>
        <xsd:element name="set" type="set"/>
      </xsd:sequence>
      <xsd:attribute name="name" type="xs:string"/>
    </xsd:complexType>

    I can't figure out how to make a union of the two. I'm beginning
    to think that this is non-deterministric, or in some other
    way a bad design.

--
Alan Gutierrez -