checking sequence inside processing-instruction

Hai,

I am having some processing instructions which will appear like this.

<?PAGEBREAK id="P001"?>
-------------------
-----------------
<?PAGEBREAK id="P002"?>
-------------
---------------
<?PAGEBREAK id="P003"?>
--------------------
--------------------
<?PAGEBREAK id="P004"?>
------------------------
------------------------
<?PAGEBREAK id="P006"?>


the result should say id="P006" is out of sequence.

<xsl:template match="processing-instruction()">
     <xsl:for-each select="processing-instruction()/name()">
        <xsl:if test="@id != following-sibling::processing-instruction()/@id"/>
           <xsl:message>following-sibling::processing-instruction()/@id
is out of sequence</xsl:message>
        </xsl:if>
     </xsl:for-each>
<xsl:template>

When i compile this sheet with saxon9b, it is showing error as
processing-instruction can not select anything.

Please help me in solving this problem.

Regards,
Ganesh