I reported this bug yesterday on

  http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=683353

and I could reproduce it after recompiling libxslt from the GIT repository.

Consider the following stylesheet:

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:param name="var"/>
<xsl:key name="key" match="*[@id != $var]" use="''"/>
</xsl:stylesheet>

The XSLT 1.0 specifications say in 12.2:

  It is an error for the value of either the use attribute or the
  match attribute to contain a VariableReference.

and in 17:

  A conforming XSLT processor must signal any errors except for
  those that this document specifically allows an XSLT processor
  not to signal.

So, since the match attribute contains $var, one would expect an error to be signaled. But:

ypig:~> ~/software/libxslt/xsltproc/xsltproc tst.xsl tst.xsl
<?xml version="1.0"?>




ypig:~> ~/software/libxslt/xsltproc/xsltproc --version
Using libxml 20800, libxslt 10126-GITv1.1.26-32-g8785a2f and libexslt 815
xsltproc was compiled against libxml 20800, libxslt 10126 and libexslt 815
libxslt 10126 was compiled against libxml 20800
libexslt 815 was compiled against libxml 20800