According to the Apache Xalan-Java documentation, the "select"
attribute on the "write" Redirect extension element should be
interpreted as an XPath expression, but it is handled as an attribute
value template by libxslt-1.0.2.

From http://xml.apache.org/xalan-j/extensionslib.html#redirect:

  Each of these elements includes a file attribute and/or a select
  attribute to designate the output file. The file attribute takes a
  string, so you can use it to directly specify the output file name.
  The select attribute takes an XPath expression, so you can use it to
  dynamically generate the output file name. If you include both
  attributes, the Redirect extension first evaluates the select
  attribute, and falls back to the file attribute if the select
  attribute expression does not return a valid file name.

The session shown below illustrates the problem when the XSLT stylesheet 
below (saved as "write-test.xsl") is evaluated using xsltproc from 
libxslt-1.0.2 and Xalan-Java from Java 2 SDK v1.4beta.  According to 
the Apache Xalan-Java documentation, the new filename should be "2"
and not "1+1".

========================================================================
  $ xsltproc write-test.xsl write-test.xsl
  <?xml version="1.0"?>
  <output>
        Nothing to see here, move along.
        </output>
  $ ls
  1+1  write-test.xsl
  $ rm -f 1+1
  $ java org.apache.xalan.xslt.Process -IN write-test.xsl -XSL
write-test.xsl
  <?xml version="1.0" encoding="UTF-8"?>
  <output>
        Nothing to see here, move along.
        </output>
  $ ls
  2  write-test.xsl
========================================================================

========================================================================
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:lxslt="http://xml.apache.org/xslt"
                xmlns:redirect="org.apache.xalan.xslt.extensions.Redirect"
                extension-element-prefixes="redirect"
                exclude-result-prefixes="lxslt redirect">
  <xsl:preserve-space elements="*"/>
  <xsl:output method="xml"/>
  <xsl:template match="/">
    <output>
      Nothing to see here, move along.
      <redirect:write select="1+1">
        <output>Not much here either.</output>
      </redirect:write>
    </output>
  </xsl:template>
</xsl:stylesheet>
========================================================================