Use of variables

Hi,
	I have the following stylesheet,

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:output method="html" indent="yes" />

<xsl:template match="/">
    <xsl:apply-templates/>
</xsl:template>


<xsl:template match="author">
  <xsl:variable name="ridsval" select="@rids" />
  <xsl:variable name="ridval"  select="substring-after('aff',$ridsval)"
/>
  <xsl:message><xsl:value-of select="$ridsval" /></xsl:message>
  <xsl:message><xsl:value-of select="$ridval" /></xsl:message>
  <xsl:element name="strong"><xsl:value-of select="$ridval"
/></xsl:element>
  <!--<xsl:element name="strong">
   <xsl:attribute name="{$ridval}">RID VAL</xsl:attribute>
  </xsl:element>-->
  <xsl:element name="strong">
   <xsl:attribute name="{$ridsval}">RIDS VAL</xsl:attribute>
  </xsl:element>
</xsl:template>

</xsl:stylesheet>

processing the following the following xml doc (the relevant bit)



.........
<author rids="aff1" role="corres">
  <name-cpn type="forename">Loraine</name-cpn>
  <name-cpn type="family">Day</name-cpn>
</author>
.........

The first xsl:message produces the desired result aff1
The second produces nothing (empty node set?)
The commented xsl:element gives the following error

Error while applying stylesheet
At xsl:attribute on line 17 of file:/D:/work/xsl/string-manip.xsl:
Invalid attribute name []

I am using Saxon 5.3.2 on NT

Once I have cleared up this problem I would like to be able to construct
variable values using predicates with
regexs e.g. sort of

<xsl:template match="author">
  <xsl:variable name="ridsval" select="@rids[(letter+ digit+)]" />

does anybody know if this is possiblke or am I going in the wrong
direction?

any help would be appreciated.


Regards,
	Ben 
-- 

--------------------------
Dr Benjamin Ryan
H. Charlesworth & Co. Ltd
www.charlesworth.com
--------------------------


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