以rpc开头的方法名预留作为系统扩展，且必须不能用于其他地方。每个系统扩展都应该有相关规范文档，所有系统扩展都应是可选的。 * * * Copyright (C) 2007-2010 by the JSON-RPC Working Group This document and translations of it may be used to implement JSON-RPC, it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not bemodified in any way.