code: function MetaData() {
  
      // the key for the storing
      this.key = null;
      // data to store
      this.value = null;
      // temporary filename for the cached file because filenames cannot represend urls completely
      this.filename = null;
      // expirydate of the entry
      this.expires = null;
      // size of the current entry
      this.size = null;
  }
docs: helper object with meta-informations about the cached data