This is just an example how something like a Layout-Description could be edited for Silva. The "content type" DisplayDescription is not of any use by itself, but can be used to display other content objects.
The current implementation simply stacks all content objects onto each other. One could think of more complicated examples, like allowing a multi-column layout or the like. (Writing a table-editor equivalent the one for the Silva Document seems to be a non-trivial action, however.)
This product also adds example "summary" views for the Silva Document and the Silva Demo Object. Especially the summary view for the Document is somewhat silly, but it should demonstrate how one could define a shorter display suitable for display a content in a listing.