请问diploma supplement是什么，怎么操作呢？

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各位前辈，小弟最近准备申请挪威的博士，然后遇到招聘的网站上有这么一句话，不太懂，请各位前辈指教。谢谢

Candidates from universities outside Norway are welcome to apply and are requested to enclose a Diploma Supplement or a similar document which describes in detail the study and grade system as well as the rights for further studies associated with the obtained degree：还另外附了个网址http://ec.europa.eu/education/policies/rec_qual/recognition/diploma_en.html

请问这个Diploma supplement 是为何物？需要怎么办理呀。是要公正学位证和毕业证吗？

请指教，O(∩_∩)O谢谢，祝大家都能飞跃成功！