[xsl] What does this XPath expression mean ?

Subject: [xsl] What does this XPath expression mean ?
From: "Z W" <mpc8250@xxxxxxxxx>
Date: Sat, 22 Mar 2008 04:27:53 -0700
Hi
Could someone be kind to help me breaking down the XPath to explain
what the expression means ?

<xsl:for-each select="/testResults/*[not(@label = preceding::*/@label)]">

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