Nextcloud extension to WebDAV?

When I make a call to the WebDAV API, Nextcloud returns a few custom namespaces:

'xmlns:d': 'DAV:',
'xmlns:s': 'http://sabredav.org/ns',
'xmlns:cal': 'urn:ietf:params:xml:ns:caldav',
'xmlns:cs': 'http://calendarserver.org/ns/',
'xmlns:card': 'urn:ietf:params:xml:ns:carddav',
'xmlns:oc': 'http://owncloud.org/ns',
'xmlns:nc': 'http://nextcloud.org/ns'

And I’m wondering is there any information about the custom properties or methods that Nextcloud provide (for example under oc: or nc: )?

The doc implies that Nextcloud simply supports the full WebDAV spec but I guess it does a bit more. For example the errors have custom info from SabreDAV.