如何像javascript中的日期函数一样在xslt格式中字符串数字转换成日期？

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/">
    <xsl:variable name="dateString" select="'20220101'" /> <!-- 假设要转换的字符串为 '20220101' -->
    <xsl:variable name="year" select="substring($dateString, 1, 4)" />
    <xsl:variable name="month" select="substring($dateString, 5, 2)" />
    <xsl:variable name="day" select="substring($dateString, 7, 2)" />
    <xsl:variable name="formattedDate" select="concat($year, '-', $month, '-', $day)" />
    <xsl:variable name="convertedDate" select="xs:date($formattedDate)" />

    <convertedDate>
      <xsl:value-of select="$convertedDate" />
    </convertedDate>
  </xsl:template>
</xsl:stylesheet>