Function converting RFC 2822 date to xsd:dateTime

Hi,

I have an XSLT 2.0 task where I'm parsing email Date headers defined
in RFC 2822 and converting them to xsd:dateTime.

Below is a function that converts between the two. I wanted to hear if
there are improvements that could be made?

    <xsl:function name="aex:rfc2822dateTime-to-dateTime" as="xs:dateTime">
        <xsl:param name="date-time" as="xs:string"/> <!-- Tue, 9 Apr
2019 00:07:24 +1200 (NZST) -->
        <xsl:variable name="months" select="'Jan', 'Feb', 'Mar',
'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'"
as="xs:string*"/>
        <xsl:analyze-string select="$date-time"
            regex="^(?:(Sun|Mon|Tue|Wed|Thu|Fri|Sat),\s+)?(0[1-9]|[1-2]?[0-9]
|3[01])\s+(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)\s+(19[0-9]{{2}}|[
2-9][0-9]{{3}})\s+(2[0-3]|[0-1][0-9]):([0-5][0-9])(?::(60|[0-5][0-9]))?\s+([-
\+][0-9]{{2}}[0-5][0-9]|(?:UT|GMT|(?:E|C|M|P)(?:ST|DT)|[A-IK-Z]))(\s+|\(([^\(
\)]+|\\\(|\\\))*\))*$">
            <xsl:matching-substring>
                <xsl:sequence
select="xs:dateTime(concat(format-number(xs:integer(regex-group(4)),
'0001'), '-', format-number(index-of($months, regex-group(3)), '01'),
'-', format-number(xs:integer(regex-group(2)), '01'), 'T',
format-number(xs:integer(regex-group(5)), '01'), ':',
format-number(xs:integer(regex-group(6)), '01'), ':',
format-number(xs:integer(regex-group(7)), '01'),
substring(regex-group(8), 1, 3), ':', substring(regex-group(8), 4,
2)))"/>
            </xsl:matching-substring>
            <xsl:non-matching-substring>
                <xsl:message>Invalid RFC 2822 datetime: <xsl:value-of
select="$date-time"/></xsl:message>
            </xsl:non-matching-substring>
        </xsl:analyze-string>
    </xsl:function>

The regex pattern is taken from
https://stackoverflow.com/questions/9352003/rfc-2822-date-regex

Martynas
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