Hello my helpers :-)

I have a Problem with a sitmap and the Tabindexes. I want to give each Sitemapnode in a the Web.sitemap thier own tabindex, but it does not function.
CODE:
<?xml version="1.0" encoding="utf-8" ?>
<siteMap xmlns="http://schemas.microso ft.com/AspNet/SiteMap-File-1.0" >

<siteMapNode title="root" description="">...