It applies to the field of law which becomes wider and wider . at first it is only the principle obligors must obey to perform the obligations to obligees and it is established as a fundemental principle in the private law gradually 它已由最初债务人履行债务的原则，逐渐确立为私法的一项基本原则，且其地位日隆，被学者们称为私法领域的“帝王原则” ，并逐渐向公法领域渗透。
