<schema

xmlns="http://www.w3.org/2001/XMLSchema" 
targetNamespace="http://FOO"
xmlns:foo="http://FOO">

      <element name="foo" type="foo:fooType" nillable="false" />

      <complexType name="fooType" mixed="true">
              <simpleContent>
                      <extension base="string" />
              </simpleContent>
      </complexType>

</schema>