How to escape string literals in XSLT which appear inside JavaScript function calls:-
<xsl:variable name="apos">'</xsl:variable><xsl:if test="data[@alias='popupMessage'] != ''"><xsl:attribute name="onclick"><xsl:text>return window.confirm('</xsl:text><xsl:value-of select="umbraco.library:Replace(data[@alias='popupMessage'], $apos, concat('\',$apos))" disable-output-escaping="yes" /><xsl:text>');</xsl:text></xsl:attribute></xsl:if>