Multiple elements with same name in XML and want to change value of one specific element only based on one condition using xslt

Question

Input XML

<?xml version="1.0"?>
<Response>
  <TroubleResponse>
    <Check>
      <DStatus>
        <GID>123456789</GID>
        <FLAG/>
      </DStatus>
      <DStatus>
        <GID>222233333</GID>
        <FLAG/>
      </DStatus>
      <DStatus>
        <GID>5555777788</GID>
        <FLAG/>
      </DStatus>
    </Check>
    <RAM>
      <Details>
        <RAMID>5555777788</RAMID>
      </Details>
    </RAM>
  </TroubleResponse>
</Response>

My question is:
I want to update the element FLAG value as TRUE where element RAMID value matches with element GID value.

How can I achieve this using XSLT?

Answer 1

Use the identity template in combination with this template

<xsl:template match="FLAG[../GID = ../../../RAM/Details/RAMID]">
    <xsl:copy>TRUE</xsl:copy>
</xsl:template>

The identity template for XSLT-1.0 is

<!-- Identity template -->
<xsl:template match="node()|@*">
  <xsl:copy>
    <xsl:apply-templates select="node()|@*" />
  </xsl:copy>
</xsl:template> 

The combination of both achieves the desired result.
If you can XSLT-2.0 or above, you can replace the identity template with

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