What is legally allowed for an ex-employer to say to a new employer about your previous employment?

How much can a previous employer say about performance, why you left, and your position? I understand for most companies maintain the policy or the theory to get as much information as you can when inquiring about somebody, but give as little as possible when somebody calls to ask about a previous employee. What... show more How much can a previous employer say about performance, why you left, and your position? I understand for most companies maintain the policy or the theory to get as much information as you can when inquiring about somebody, but give as little as possible when somebody calls to ask about a previous employee. What are the parameters of what they are allowed to say legally and in regards to liability? Does anyone in a Human Resource role know and how much gray area can occur?
Update: I understand that they are only supposed to give your date of hire and leave, and job title, but I wonder how often companies give more than that? I would like to really hear from somebody that is in HR and can be honest about what has been said from experience.
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