#39 Apps can't tell how invoked

Applications can't tell if they've been invoked as a 'document
proper' or as a subdocument.

For instance, an application
that wanted to provide a convenience 'get properties' link should
only provide that link if the document in question is a proper
document - not if it's a subdocument.

Or, another example
would be the opposite use - the contact viewer might wish to provide a
'Create a new contact with this information' link when you're viewing
a contact - good for like clicking on an attached vcard to an email. It
would only want to do so if the vcard in question was NOT a proper
document.