use of xs:annotation outside of schema

Is it OK to re-use something like xs:annotation for my own schemas?  That
is, I want to allow annotation of elements in my instance documents, and it
seems xs:annotation provides just what I want.  For example,

  <xs:complexType name = "my-annotated">
      <xs:sequence>
          <xs:element ref = "xs:annotation" minOccurs = "0"/>
          <xs:element ref = "my-content"/>
      </xs:sequence>
  </xs:complexType>

If it is OK, do I need an <import> for the XML Schema namespace?  Seems that
I don't since the processor already knows all about that namespace.

xan

Xan Gregg
TIBCO Software, Inc.
www.tibco.com