docs: function encode(cache, API_URL, obj) {
    if (!obj) return null;
    if (!obj.href) return obj;
  
    var href = API_URL ?
      pack(obj.href, API_URL) :
      obj.href;
  
    var cached = cache.get(href);
    if (cached) return cached;
  
    var encoded = base64.encode(new Buffer(href)).toString();
    cache.set(href, encoded);
    return encoded;
  }