xsl:number value="id(@ref)" ?

For generating links to numbered images in hypertext
I'm using ID referencing. Accessing the children of a
referenced node works fine with XT, but an xsl:number
element using the reference returns always zero. Is
something wrong with my code?

-------SOURCE-------
<!DOCTYPE myroot [
  <!ELEMENT see (#PCDATA)>
  <!ELEMENT dest (#PCDATA)>
  <!ATTLIST see ref CDATA #REQUIRED>
  <!ATTLIST dest id ID #REQUIRED> ]>
<myroot>
  <see ref="D2"/>
  <dest id="D1">Node D1</dest>
  <dest id="D2">Node D2</dest>
  <dest id="D3">Node D3</dest>
</myroot>

------STYLESHEET------
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version
="1.0">
  <xsl:template match="//see">
    'see' finds destination '<xsl:value-of select="id(@ref)"/>',
    whose position is: <xsl:number value="id(@ref)"/>.
  </xsl:template>
  <xsl:template match="text()"/>
</xsl:stylesheet>

--------RESULT--------
'see' finds destination 'Node D2',
whose position is: 0.

---------------------
Thanks in advance
Michael