How can I convert a string to upper- or lower-case with XSLT?

In XSLT 1.0 the upper-case() and lower-case() functions are not available.
If you’re using a 1.0 stylesheet the common method of case conversion is translate():

<xsl:variable name="lowercase" select="'abcdefghijklmnopqrstuvwxyz'" />
<xsl:variable name="uppercase" select="'ABCDEFGHIJKLMNOPQRSTUVWXYZ'" />


<xsl:template match="https://stackoverflow.com/">
  <xsl:value-of select="translate(doc, $lowercase, $uppercase)" />
</xsl:template>