<xsl:if test="not(@foo = preceding-sibling::*[@foo][1]/@foo)">

to only reveal certain content if it is there is a difference
between attribute values found in the node immediately preceeding
the current node.

It seemed to work for a while, but now seems to show the value of
the first node's attribute.

    <xsl:if test="preceding-sibling::*[@foo] and
                  not(@foo = preceding-sibling::*[@foo][1]/@foo)">

T:\ftemp>type goddard.xml
<?xml version="1.0"?>
<doc>
 <test foo="a" item="1"/>
 <test foo="b" item="2"/>
 <test foo="b" item="3"/>
 <test foo="c" item="4"/>
 <test foo="d" item="5"/>
 <test foo="d" item="6"/>
</doc>
T:\ftemp>type goddard1.xsl
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="1.0">

<xsl:template match="/">                         <!--root rule-->
  <xsl:for-each select="//test">
    <xsl:if test="not(@foo = preceding-sibling::*[@foo][1]/@foo)">
Found: <xsl:value-of select="@foo"/> in <xsl:value-of
                                                  select="@item"/>
    </xsl:if>
  </xsl:for-each>
</xsl:template>

T:\ftemp>xt goddard.xml goddard1.xsl
<?xml version="1.0" encoding="utf-8"?>

Found: a in 1
Found: b in 2
Found: c in 4
Found: d in 5
T:\ftemp>type goddard2.xsl
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="1.0">

<xsl:template match="/">                         <!--root rule-->
  <xsl:for-each select="//test">
    <xsl:if test="preceding-sibling::*[@foo] and
                  not(@foo = preceding-sibling::*[@foo][1]/@foo)">
Found: <xsl:value-of select="@foo"/> in <xsl:value-of
                                                  select="@item"/>
    </xsl:if>
  </xsl:for-each>
</xsl:template>

T:\ftemp>xt goddard.xml goddard2.xsl
<?xml version="1.0" encoding="utf-8"?>

Found: b in 2
Found: c in 4
Found: d in 5
T:\ftemp>rem

--
G. Ken Holman                    mailto:gkholman@xxxxxxxxxxxxxxxxxxxx
Crane Softwrights Ltd.             http://www.CraneSoftwrights.com/s/
Box 266, Kars, Ontario CANADA K0A-2E0   +1(613)489-0999   (Fax:-0995)
Web site: XSL/XML/DSSSL/SGML services, training, libraries, products.
Book: Practical Transformation Using XSLT and XPath ISBN1-894049-05-5
Article:          What is XSLT? http://www.xml.com/pub/2000/08/holman
Next public instructor-led training:        2000-09-19/20,2000-10-03,
-          2000-10-04,2000-10-05,2000-10-09/10,2000-10-19,2000-11-12,
-                                            2000-12-03/04,2001-01-27