Such information may not only be optional, but may not even be relevant for a particular use of it, such as in the retrieve operation where only the member identifier would be required.
这些信息不仅能为可选的，而且甚至还能与其特定用法相关，例如在检索操作中就只需要成员标识符。
2
When the member is invoked, optional arguments can be omitted.
在调用该成员时，可选参数可以忽略。
3
Returns a string containing the Login server URL for a member, along with the optional information sent to the Login server in the query string.