In addition to the normal menu definition, you can define rules to enable the conditional visibility of menu entries.
除了普通的菜单定义，您还可以定义规则来启用菜单项的有条件可视性。
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The only vexing conditional in Listing 15 happens to be the first one, which attempts to verify if the message is truly a definition query and not one of the other possible combinations such as is...