xsl:with-param is processed as a param in a xsl:template, although
a corresponding xsl:param was not declared.
The following example does not produce an error, but it should:

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

  <xsl:template match="/">
    <xsl:call-template name="foo">
      <xsl:with-param name="bar" select="'bar'"/>
    </xsl:call-template>
  </xsl:template>

  <xsl:template name="foo">
    <xsl:value-of select="$bar"/>
  </xsl:template>

</xsl:stylesheet>