docs: function PubSub(stats) {
  
    // ref to statistics so they can be updated
    // as subscriptions change
    this._stats = stats;
  
    // normal channels
    this._channels = {};
  
    // pattern channels
    this._patterns = {};
  
    this._count = {
      channels: {
        total: 0,       // total number of channels
        subscribers: 0, // total subscribers across all channels
      },
      patterns: {
        total: 0,       // total number of patterns
        subscribers: 0, // total subscribers across all patterns
      }
    }
  }