This is a browseable view of the IVOA registry as a tree structure. Links ending in a slash lead to branches; links with no slash at the end lead to resource documents for the things registered.
The branches are represented as web pages with further links while the resource documents are in XML. If you get a resource document with a utility such as wget you get the actual XML text from the registry. If you view it in a web browser you see a view of the text turned into HTML for ease of reading; use the show source function in your browser to see the original XML.