SAX-ext proposal #1: standalone flag

[David Brownell <david-b@pacbell.net>]

Document infoset extension

- One of the infoset properties for documents is not supported by
  SAX2:  whether it is standalone.

PROPOSAL

    - Define a new standard feature ID:

 http://xml.org/sax/features/is-standalone
   Read-only; only visible while parsing

   If true, the document was declared as standalone.
   If false, it was either declared as standalone='no',
   or no standalone declaration was present.
    
QUESTIONS:

    - Is it necessary to distinguish "no standalone decl"?  If so
      accessing that feature could throw SAXNotSupportedException.
      It's a bit more work from parsers to track that.