public function addVariables()
 {
     $s = new Stylesheet();
     $s->addVariable('session');
     $s->addVariable('language');
     $variables = $this->getElementsByTagName($s->root, 'xsl:variable');
     $this->assertEquals('<xsl:variable name="session"></xsl:variable>', trim($variables->get(0)->getSource(INDENT_NONE)));
     $this->assertEquals('<xsl:variable name="language"></xsl:variable>', trim($variables->get(1)->getSource(INDENT_NONE)));
 }