code: function addChainWatcher(obj, keyName, node) {
    if (!obj || ('object' !== typeof obj)) return; // nothing to do
    var m = metaFor(obj);
    var nodes = m.chainWatchers;
    if (!nodes || nodes.__emberproto__ !== obj) {
      nodes = m.chainWatchers = { __emberproto__: obj };
    }
  
    if (!nodes[keyName]) { nodes[keyName] = {}; }
    nodes[keyName][guidFor(node)] = node;
    Ember.watch(obj, keyName);
  }
docs: .......................................................... CHAIN  @private