code: function iterDeps(method, obj, depKey, seen, meta) {
  
    var guid = guidFor(obj);
    if (!seen[guid]) seen[guid] = {};
    if (seen[guid][depKey]) return;
    seen[guid][depKey] = true;
  
    var deps = meta.deps;
    deps = deps && deps[depKey];
    if (deps) {
      for(var key in deps) {
        if (DEP_SKIP[key]) continue;
        method(obj, key);
      }
    }
  }
docs: skip some keys and toString @private