Where the contract has expired but the duration of the patent relating to the imported technology has not expired, the relevant stipulations of the Patent Law of People's Republic of China shall govern.

问：where这里引导的是什么从句？where在从句中充当什么句子成分？是不是放在主句后从句就不用逗号

了，而放在主句前的从句一定要用逗号隔开，这又是为什么？