It is a hidden rule in the workplace.

这是职场的潜规则嘛。

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The first column, which lists the subject, is hidden and used only for setting up a sorting rule (see figure 2).

第一列列出主题，此列是隐藏的，仅用于设置排序规则(参见图2)。

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Strict rule to follow: Never give away your phone number or address. Even the email address should remain hidden at least until the first meeting.

必须遵守的原则：坚决不泄漏你的手机号码或是地址。甚至连电子邮件的地址也至少在第一次会面之后再给出去。

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But Edwin avoids consuming caffeine as a rule, and the pallet of Frava had been collecting dust, hidden in one of his cabinets ever since.

FORBES: The Product