move element from an xml file to another xml element using xslt-3

Question

Given the following example xml file:

<?xml version="1.0"?>
        <catalog>
           <book id="bk101">
              <author>Gambardella, Matthew</author>
              <title>XML Developer's Guide</title>
              <genre>Computer</genre>
              <price>44.95</price>
              <publish_date>2000-10-01</publish_date>
              <description>An in-depth look at creating applications 
              with XML.</description>
           </book>
           <book id="bk102">
              <author>Ralls, Kim</author>
              <title>Midnight Rain</title>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-12-16</publish_date>
              <description>A former architect battles corporate zombies, 
              an evil sorceress, and her own childhood to become queen 
              of the world.</description>
           </book>
           <book id="bk103">
              <title>Maeve Ascendant</title>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-11-17</publish_date>
              <description>After the collapse of a nanotechnology 
              society in England, the young survivors lay the 
              foundation for a new society.</description>
           </book>
        </catalog>

I need to merge all title elements into the author element, by a rule: If the author element already exists, then the title element's value will be inserted in the author record, using a separator ie a | character. If there is not an author element in the record, the title element would become the author element. Desired output:

 <?xml version="1.0"?>
        <catalog>
           <book id="bk101">
              <author>Gambardella, Matthew | XML Developer's Guide</author>
              <genre>Computer</genre>
              <price>44.95</price>
              <publish_date>2000-10-01</publish_date>
              <description>An in-depth look at creating applications 
              with XML.</description>
           </book>
           <book id="bk102">
              <author>Ralls, Kim | Midnight Rain</author>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-12-16</publish_date>
              <description>A former architect battles corporate zombies, 
              an evil sorceress, and her own childhood to become queen 
              of the world.</description>
           </book>
           <book id="bk103">
              <author>Maeve Ascendant</author>
              <genre>Fantasy</genre>
              <price>5.95</price>
              <publish_date>2000-11-17</publish_date>
              <description>After the collapse of a nanotechnology 
              society in England, the young survivors lay the 
              foundation for a new society.</description>
           </book>
        </catalog>

How the above result could be achieved using xslt-3?

Answer 1

What I would do is strip the existing author element and replace the title element with a new author element.

The value of the new author element would be a string-join of the original author (if it exists) and the current title value separated by | .

Example...

<xsl:stylesheet version="3.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output indent="yes"/>
  <xsl:strip-space elements="*"/>

  <xsl:mode on-no-match="shallow-copy"/>

  <xsl:template match="author"/>

  <xsl:template match="title">
    <author>
      <xsl:value-of select="string-join((../author,.),' | ')"/>
    </author>
  </xsl:template>

</xsl:stylesheet>

Note: This would work as XSLT 2.0 too if you replaced xsl:mode with the identity transform .