your question is somewhat under-specified (and xslt has no access to
the tags in the document, only the element structure) but I think you
want something like

<xsl:for-each-group select="*" group-starting-with="p|title">
<xsl:choose>
 <xsl:when  test="self::title">
   <xsl:copy-of select="current-group()"/>
 <xsl:when>
 <xsl:otherwise>
   <group>
   <xsl:copy-of select="current-group()"/>
   </group>
 </xsl:otherwise>
 <xsl:choose>
   

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