XML anatomy

[Bric]

In the denemo XML I am seeing the <rhythms>...</rhythms> section (no pun intended)  which contains three <rhythm... > ... </rhythm> nodes.  I can't figure out what this represents.  (Is there any documentation elaborating on the XML structure?)  :

<rhythms>

    <rhythm lilypond="">
        <objects>
           <chord show="true" id="id0">
                <duration base="whole"></duration>
                <directives>
                   <directive>
                   <tag>Duration</tag>
                   <prefix>\longa </prefix>
                   <graphic_name>emmentaler</graphic_name>
                   <override>6</override>
                </directive>
             </directives>
             <ticks>6144</ticks>

            <notes>
               <note id="id1">
                <middle-c-offset>1</middle-c-offset>
            </note>
           </notes>
         </chord>
      </objects>
   </rhythm>

.....