Caminho relativo XSLT

<fo:block>
                                            <fo:external-graphic>
                                                <xsl:attribute name="src">
                                                    <xsl:text>url(</xsl:text>
                                                    <xsl:call-template name="double-backslash">
                                                        <xsl:with-param name="text">

                                                             erro
                                                            <xsl:value-of select="string(&apos;..\config\resources\Logo.jpg&apos;)" />


                                                             funciona
                                                            <xsl:value-of select="string(&apos;C:\config\resources\Logo.jpg&apos;)" />


                                                        </xsl:with-param>
                                                    </xsl:call-template>
                                                    <xsl:text>)</xsl:text>
                                                </xsl:attribute>
                                            </fo:external-graphic>
                                        </fo:block>