JSON compatiiblity of YAML

Hi all,

The specification has the next statement in section 1.3.

> every JSON file is also a valid YAML file. 

However, from the thread,

  [Yaml-core] YAML ain't a superset of JSON 
  From: Jakob Voss <jakob.voss@ni...> - 2009-06-06 14:05,
  http://sourceforge.net/mailarchive/forum.php?thread_name=4A2A69F8.4000902%40nichtich.de&forum_name=yaml-core
  http://sourceforge.net/mailarchive/forum.php?thread_name=1244318281.4601.11.camel%40nero&forum_name=yaml-core
  http://sourceforge.net/mailarchive/forum.php?thread_name=1244468527.4601.25.camel%40nero&forum_name=yaml-core

I learned the following.

- JSON defines that the keys in a mapping node SHOULD be unique 
  while YAML requires they MUST.
- So, a YAML parser is a JSON parser.
- But not every valid JSON document is a valid YAML document.

If my understanding is correct, I would like to have the spec 
to describe this point clearer or to permit duplicated keys 
in a mapping node.

Best,
Osamu TAKEUCHI

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