Merge siblings

merge-siblings

<xsl:transform version="2.0"
               xmlns:fn="tag:[email protected],2019:merge-siblings"
               xmlns:xs="http://www.w3.org/2001/XMLSchema"
               xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

  <xsl:function name="fn:sibling-group-key" as="xs:string">
    <xsl:param name="node" as="node()"/>

    <xsl:value-of select="generate-id(fn:sibling-group($node)[1])"/>

  </xsl:function>

  <xsl:function name="fn:sibling-group" as="node()+">
    <xsl:param name="node" as="node()"/>

    <xsl:sequence select="fn:sibling-group-head($node) union fn:sibling-group-tail($node)"/>

  </xsl:function>

  <xsl:function name="fn:sibling-group-tail" as="node()+">
    <xsl:param name="node" as="node()"/>

    <xsl:variable name="following" select="$node/following-sibling::node()"/>
    <xsl:variable name="preceding" select="$node/preceding-sibling::node()"/>

    <xsl:sequence select="($node, $following[every $n in (preceding-sibling::node() except $preceding) satisfies fn:is-sibling-group-member($n)])"/>

  </xsl:function>

  <xsl:function name="fn:sibling-group-head" as="node()+">
    <xsl:param name="node" as="node()"/>

    <xsl:variable name="following" select="$node/following-sibling::node()"/>
    <xsl:variable name="preceding" select="$node/preceding-sibling::node()"/>

    <xsl:sequence select="($preceding[every $n in (following-sibling::node() except $following) satisfies fn:is-sibling-group-member($n)], $node)"/>

  </xsl:function>

  <xsl:function name="fn:is-sibling-group-member" as="xs:boolean">
    <xsl:param name="node" as="node()?"/>
    <xsl:sequence select="false()"/>
  </xsl:function>

</xsl:transform>