Changing local customizations depending on XSLT processor?

Is it possible to use XSLT conditionals and xsl:vendor or
xsl:vendor-url, to only set values when a particular XSLT processor is
used?

Specifically, I would like to only set these variables when using
Saxon or Xalan, but not while running xsltproc:

  <xsl:param name="use.extensions" select="'1'" />
  <xsl:param name="textinsert.extension" select="'1'" />

Thanx!


- Steinar