cmisra:content mediatype needs explanation

3.5.3.6 cmisra:content also in 4.2 Entries and 9.2.2 Document Entry PUT and CMIS-RestAtom.xsd

• The cmisra:content element has a mediatype element. What is its semantics?
  o I assume it is a media type (i.e. text/html or whatever)? Or is it like the atom:content/type element which can be "text", "html", "xhtml" or a media type?
  o It is not a required element per the schema, so is there a default value or default action for the server to take when it is not present?