Side-effect of xsl:sort on indentation

Question

I need to sort elements BillOfMaterialIem based on value of attribute billOfMaterialItemID Example :

<?xml version="1.0" encoding="UTF-8"?>
<PackageData documentCreateDate="2019-10-03" documentModificationDate="2019-10-03">
  <Items>
    <Item itemID="416664">
      <BillOfMaterial>
        <BillOfMaterialItem billOfMaterialItemID="417230" />
        <BillOfMaterialItem billOfMaterialItemID="417231" />
        <BillOfMaterialItem billOfMaterialItemID="416664-01"/>
        <BillOfMaterialItem billOfMaterialItemID="110424" />
      </BillOfMaterial>
    </Item>
  </Items>
</PackageData>

This is ok to copy everything and filter empty atttributes :

<xsl:template match="node()">
  <xsl:copy>
    <xsl:apply-templates select="@*|node()">
    </xsl:apply-templates>
  </xsl:copy>
</xsl:template>
<xsl:template match="@*">
  <xsl:if test="string-length(.)!=0">
    <xsl:copy-of select="."/>
  </xsl:if>
</xsl:template>

Here is the template specific to element BillOfMaterial :

<xsl:template match="BillOfMaterial">
  <xsl:copy>
    <xsl:apply-templates select="BillOfMaterialItem" >
      <xsl:sort select="@billOfMaterialItemID"/>
    </xsl:apply-templates>
  </xsl:copy>
</xsl:template>

Elements are sorted as expected but identation is killed in the output - despite indent="yes". I don't get the reason for this side-effect.

What do I miss ?

Answer 1

<xsl:strip-space elements="*"/> makes it work

Thank you, michael.hor257k