XSLT create nested structure (table of content-style) when there is none

Question

This is what it looks like now

<Titre_2>first level 01</Titre_2>
<Titre_2>second level 01</Titre_2>
<Titre_2>third level 01</Titre_2>
<Titre_3_ch1>deepest01</Titre_3_ch1>
<Titre_3_ch1>deepest02</Titre_3_ch1>
<Titre_3_ch1>deepest03</Titre_3_ch1>
<Titre_2>third level 02</Titre_2>
<Titre_3_ch1>deepest04</Titre_3_ch1>
<Titre_3_ch1>deepest05</Titre_3_ch1>
<Titre_3_ch1>deepest06</Titre_3_ch1>
<Titre_2>second level 02</Titre_2>
<Titre_2>third level 03</Titre_2>
<Titre_3_ch2>deepest07</Titre_3_ch2>
<Titre_3_ch2>deepest08</Titre_3_ch2>
<Titre_3_ch2>deepest09</Titre_3_ch2>
<Titre_3_ch2>deepest10</Titre_3_ch2>

and this is an example of the structure it should get:

<TOC.BLK>
  <TOC.ITEM>
    <ITEM.CONT>first level 01</ITEM.CONT>
  </TOC.ITEM>
  <TOC.BLK>
    <TOC.HD>
      <TOC.HD.CONT>second level 01</TOC.HD.CONT>
    </TOC.HD>
    <TOC.BLK>
      <TOC.HD>
        <TOC.HD.CONT>third level 01</TOC.HD.CONT>
      </TOC.HD>
      <TOC.ITEM>
        <ITEM.CONT>deepest 01</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 02</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 03</ITEM.CONT>
      </TOC.ITEM>
    </TOC.BLK>
    <TOC.BLK>
      <TOC.HD>
        <TOC.HD.CONT>third level 02</TOC.HD.CONT>
      </TOC.HD>
      <TOC.ITEM>
        <ITEM.CONT>deepest 04</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 05</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 06</ITEM.CONT>
      </TOC.ITEM>
    </TOC.BLK>
    <TOC.BLK>
      <TOC.HD>
        <TOC.HD.CONT>third level 03</TOC.HD.CONT>
      </TOC.HD>
      <TOC.ITEM>
        <ITEM.CONT>deepest 07</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 08</ITEM.CONT>
      </TOC.ITEM>
    </TOC.BLK>
  </TOC.BLK>
  <TOC.BLK>
    <TOC.HD>
      <TOC.HD.CONT>second level 02</TOC.HD.CONT>
    </TOC.HD>
    <TOC.BLK>
      <TOC.HD>
        <TOC.HD.CONT>third level 03</TOC.HD.CONT>
      </TOC.HD>
      <TOC.ITEM>
        <ITEM.CONT>deepest 09</ITEM.CONT>
      </TOC.ITEM>
      <TOC.ITEM>
        <ITEM.CONT>deepest 10</ITEM.CONT>
      </TOC.ITEM>
    </TOC.BLK>
  </TOC.BLK>
</TOC.BLK>

Or to put it differently: the number of sequential titles with the same name dictates the levels they are in

So what has to happen: everything that starts with <Titre_3> has to get <ITEM.CONT> around it

every <Titre_2> (this is obviously the tricky part) has to be evaluated:

traversing the xml from top to bottom there are 3 possible block-levels:

• 3x Titre_2
  • first one = highest level => contains all deeper levels (there is only 1 such level - so it wraps all others)
  • second one = level 2 => contains all deeper levels (wraps all level 3 blocks that follow it)
  • third one = level 3 => contains all deeper levels (<ITEM>)(wraps the deepest levels that follow it)
• 2x Titre_2
  • first one = level 2 => contains all deeper levels (wraps all level 3 blocks that follow it)
  • second one = level 3 => contains all deeper levels (wraps the deepest levels that follow it)
• 1x Titre_2
  • level 3 = contains all deeper levels(wraps the deepest levels that follow it)