How to create Incremental sequence numbers in XML using XSLT

Question

I need to generate a incremental sequence number like the one below. If you could see the sequence number attribute below, it doesn't have a proper order, in some places it occurs in descendant node and some places in different order. Is there any generic code to generate this sequence number.

Currently, I tried using the below ways but these didn't work. Any help would be appreciated.

1. xsl:value-of select="preceding-sibling::@[SeqNum]/@n"
2. SeqNum="{format-number(count(preceding@SeqNum)+1,'0000')}"

Sample XML:

<act>
    <ActAssociation ***SeqNum="1"***>
        <InitialRptIndicator>Y</InitialRptIndicator>
    </ActAssociation>
    <Party ***SeqNum="2"***>
        <ActPartyTypeCode>35</ActPartyTypeCode>
        <PartyName ***SeqNum="3"***>
            <PartyNameTypeCode>L</PartyNameTypeCode>
        </PartyName>
    </Party>
    <Party SeqNum="4">
        <PartyName SeqNum="5">
            <fc2:PartyNameTypeCode>L</fc2:PartyNameTypeCode>
        </PartyName>
    </act>

Answer 1

If you add the attributes by hard coding them I think the easiest solution in XSLT 2 and later is to do that in a variable so that you have a temporary tree, and then you push that tree through a mode that uses <xsl:number count="*[@SeqNum]" level="any"/> :

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    exclude-result-prefixes="xs"
    version="3.0">

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

  <xsl:output method="xml" indent="yes"/>

  <xsl:variable name="doc1">
      <root>
          <foo SeqNum=""/>
          <bar>
              <foobar SeqNum=""/>
          </bar>
          <baz SeqNum="">
              <whatever/>
          </baz>
      </root>
  </xsl:variable>

  <xsl:template match="/">
      <xsl:apply-templates select="$doc1/node()"/>
  </xsl:template>

  <xsl:template match="*/@SeqNum">
      <xsl:attribute name="{name()}">
          <xsl:number count="*[@SeqNum]" level="any"/>
      </xsl:attribute>
  </xsl:template>

</xsl:stylesheet>

See https://xsltfiddle.liberty-development.net/eiZQaFu/2 , it is XSLT 3 but for XSLT 2 you simply need to replace the xsl:mode by the identity transformation template .