规定的唯一约定是返回0应该表示成功而返回非零值表示失败。
The only convention prescribed is that 0 should be returned for success and a nonzero value for failure.
如果阻止了请求，就会模拟表示失败的Content Manager响应，这导致发出调用的客户机显示错误，向用户表明此操作已经被阻止。
If a request is blocked, a Content Manager response indicating a failure is simulated causing the calling client to display an error which indicates that this operation has been prevented.
它尝试解决通常在以下情况下发生的问题：某个函数返回1以表示成功，返回0以表示失败，而另一个函数返回1以表示成功，返回- 1以表示失败。
It tries to address the problem that usually occurs when a function returns 1 for success and 0 for failure and another function returns 1 for success and -1 to indicate failure.
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