xpath - getting precedeing-sibling::element/@id ?

using xpath, how do I find an element, with a specific
attribute (say <tab state="on">), and then grab it's
preceding and/or following element's (child or
sibling) 'id' attribute? (say <tab id="1.2.3">)

...assuming this xml:

<tab state="on">
 <tab id="1.2.3" state="off"></tab>
 <tab id="1.2.4" state="on"></tab>
</tab>



...i tried:

<xsl:variable name="prev"
select="preceding-sibling::tab[@state='on']/@id"/>

but i am getting errors.

please help!

thanks,

=====
--
Anthony E.
AP Web Design

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