• contains just paragraphs, or <supportDesc> and <layoutDesc>

<objectDesc form="codex">
<supportDesc material="mixed"><p>Early modern
<material>parchment</material> and
<material>paper</material>.</p></supportDesc>
<layoutDesc><layout ruledLines="25-32"/></layoutDesc>
</objectDesc>

Or a more complex substructure with specific elements for <support>, <extent>, <foliation>, <collation>, <condition>.

Multiple layouts may be specified:

<layoutDesc>
<layout ruledLines="25-32">
<p><locus from="1r-202v"/> 
<locus from="210r-212v"/>
Between 25 and 32 ruled lines.</p>
</layout>
<layout ruledLines="34-50">
<p><locus from="203r-209v"/>Between 34 and 50 ruled lines.</p>
</layout></layoutDesc>