code: function(space, type, path, value, index) {
  		// console.log('context.notifyUpstream : ', space, type, path, value, index);
  		for (var i = 0, len = space._upstreams.length; i < len; ++i) {
  			var upstream = space._upstreams[i];
  			if (!upstream) {
  				// maybe it's because upstreams length has change so update it
  				// (probably a (or more) previous listener has removed some listeners through cascade)
  				len = space._upstreams.length;
  				continue;
  			}
  			// path is local to notified node. value is the modified value. index is the one from modification point.
  			upstream.call(this, value, type, path, index);
  		}
  	}
docs: notification from root to modification point.
  Normaly for internal use.