@Override
  public String toString() {
    return String.format("Key: %s, Flags: %d, TTL: %d, Size: %d\nValue: %s",
      getKey(), getItemFlags(), getTTL(), getValue().length, deserialize());
  }
Gets the value of the revid field. Only returned with a tap mutation
message.

@return The revid of the document.
src/main/java/net/spy/memcached/tapmessage/ResponseMessage.java