How to rewrite an element's attribute value using the current attribute value? - xslt-1.0

Question

I've got an almost working XSLT sample, but for some reason it adds the attribute to the parent instead of rewriting the node I am trying to rewrite.
Input XML
<Include xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<DirectoryRef Id="WEBFOLDER">
<Directory Id="dirA82847423D2E0E6780E69FEDB5941AC0" Name="web">
<Component Id="cmpADE52C2B19915F5AFB7C41166996B6C5" Guid="*">
<File Id="fil83688EC53AE556DE24B5F5444F16F6BE" KeyPath="yes" Source="$(var.SolutionDir)\Company.PCR.Blazor.dll" />
</Component>
</Directory>
</DirectoryRef>
</Fragment>
</Include>
My XSL (transformation)
<!-- patch relative paths -->
<xsl:template match="wix:File">
<xsl:attribute name="Source">
<xsl:value-of select="concat(substring(self::node()/#Source,0,19), '..\artifacts\msi\web\', substring(self::node()/#Source, 20))"/>
</xsl:attribute>
</xsl:template>
Actual output (currently transformed)
<Include xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<DirectoryRef Id="WEBFOLDER">
<Directory Id="dirA82847423D2E0E6780E69FEDB5941AC0" Name="web">
<Component Id="cmpADE52C2B19915F5AFB7C41166996B6C5" Guid="*" Source="$(var.SolutionDir)..\artifacts\msi\web\Company.PCR.Blazor.dll"/>
</Directory>
</DirectoryRef>
</Fragment>
</Include>
Expected XML output (transformed):
<Include xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Fragment>
<DirectoryRef Id="WEBFOLDER">
<Directory Id="dirA82847423D2E0E6780E69FEDB5941AC0" Name="web">
<Component Id="cmpADE52C2B19915F5AFB7C41166996B6C5" Guid="*">
<File Id="fil83688EC53AE556DE24B5F5444F16F6BE" KeyPath="yes" Source="$(var.SolutionDir)..\artifacts\msi\web\Company.PCR.Blazor.dll" />
</Component>
</Directory>
</DirectoryRef>
</Fragment>
</Include>
Can you explain why my match="wix:File" applies its attribute change to its parent?

Answer 1

If you want to modify the Source attribute, then why not make the template match the Source attribute?
<xsl:template match="wix:File/#Source">
<xsl:attribute name="Source">
<xsl:value-of select="concat(substring(., 1, 18), '..\artifacts\msi\web\', substring(., 20))"/>
</xsl:attribute>
</xsl:template>