Does XSLT support a way to modify gregorian dates? For example, if given a value using a simple date format (mm/dd/yyyy 00:00:00), I want to add 3 months to that date and return the value in the same simple date format.

In case anyone is interested, date conversion answers maybe found at http://www.dpawson.co.uk/xsl/rev2/dates.html

XSLT 2.0 has lots of support for date manipulation. But it's a good idea to use the ISO standard date format YYYY-MM-DDTHH:MM:SS (if you don't, you'll have to convert into that format before you do anything else).

There's no date/time support in XSLT 1.0 itself, but there's a date/time library at www.exslt.org which is supported by a number of implementations.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

Thanks. I have one lingering question and that is how do I modify the year using xs:dayTimeDuration? Is that possible or do I have to use another function?

<xsl:template match="/">

<xsl:variable name="date" select="date"/>
<xsl:variable name="current_date" select="bf:to-iso-date($date)"/>
<xsl:variable name="date_increase" select="string('PT5Y')"/>
<xsl:variable name="modified_date" select="string(xs:dateTime($current_date) + xs:dayTimeDuration($date_increase))"/>
<xsl:value-of select="bf:to-yyyymmdd-date($modified_date)"/>
</xsl:template>

<xsl:function name="bf:to-iso-date" as="xs:dateTime">
<xsl:param name="in" as="xs:string"/>
<xsl:sequence select="xs:dateTime(replace($in, '(\d{2})/(\d{2})/(\d{4}) ([\d:]{8})','$3-$1-$2T$4'))"/>
</xsl:function>

<xsl:function name="bf:to-yyyymmdd-date" as="xs:string">
<xsl:param name="in" as="xs:string"/>
<xsl:sequence select="xs:string(replace($in, '(\d{4})-(\d{2})-(\d{2})T([\d:]{8})','$2/$3/$1 $4'))"/>
</xsl:function>

You can do this but you need a yearMonthDuration not a dayTimeDuration (and there's no "T" in the literal):

<xsl:template match="/">

<xsl:variable name="date" select="date"/>
<xsl:variable name="current_date" select="bf:to-iso-date($date)"/>
<xsl:variable name="date_increase" select="'P5Y'"/>
<xsl:variable name="modified_date" select="string(xs:dateTime($current_date) + xs:yearMonthDuration($date_increase))"/>
<xsl:value-of select="bf:to-yyyymmdd-date($modified_date)"/>
</xsl:template>


Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference