Nested/ multi-level grouping xslt

Question

I have the below xml which I need to first group-by Requester and then for each group I need to have another group-by based on Item exists or not.

<root>
<row>
    <Requester>Tim</Requester>
    <Item>A</Item>
</row>
<row>
    <Requester>Tim</Requester>
    <Item>B</Item>
</row>
<row>
    <Requester>Tim</Requester>
    <Item/>
</row>
<row>
    <Requester>Ken</Requester>
    <Item>A</Item>
</row>

As you can see the first 3 rows have matching requester but 3rd row for Tim doesn't have Item. So there should be 2 groups for Tim.

The output I need looks like:

<root>
<row>
    <Requester>Tim</Requester>
    <Line>
        <Item>A</Item>      ---> Grouped together because Item exists. Item name may not match
        <item>B</item>
    </Line>
</row>
<row>
    <Requester>Tim</Requester>
    <Line>
        <Item/>        --> Separate group because there is no Item 
    </Line>
</row>
<row>
    <Requester>Ken</Requester>
    <Line>
        <Item>A</Item>
    </Line>
</row>

The xslt I was able to build so far:

    <xsl:template match="/">
    <root>
        <xsl:for-each-group select="root/row" group-by="Requester">
            <row>
                <Requester>
                    <xsl:value-of select="Requester[position()=1]"/>
                </Requester>
                <xsl:for-each select="current-group()">
                    <Line>
                        <Item>                        
                            <xsl:value-of select="Item"/>
                        </Item>
                    </Line>
                </xsl:for-each>
            </row>
        </xsl:for-each-group>
    </root>    
</xsl:template>

Answer 1

Try:

XSLT 3.0

<xsl:stylesheet version="3.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/root">
    <root>
        <xsl:for-each-group select="row" group-by="Requester, exists(Item/text())" composite="yes">
            <row>
                <xsl:copy-of select="Requester"/>
                <Line>
                    <xsl:copy-of select="current-group()/Item"/>
                </Line>
            </row>
        </xsl:for-each-group>
    </root>    
</xsl:template>

</xsl:stylesheet>