code: function appendAttrs(action, attrs, _updates, opts) {
    var updates = isTypeUpdates(this) ? this : (_updates || (new Updates()));
  
    if (attrs && hasKeysOnly(attrs)) {
      appendAttrsKeysOnly(action, attrs, updates, opts);
    } else if (typeof attrs === "object") {
      util.forIn(attrs, function(value, key) {
        if (value !== null && typeof value !== 'undefined')
          appendAttr(action, key, value, updates, opts);
      });
    }
    
    return updates;
  }
docs: /*
  Append action and attributes to the specified updates object.