What is the principle of promise estoppel?

The promissory estoppel rule in Anglo-American legal system is based on the overly strict theory of consideration, in order to relieve the damage caused by the reasonable trust of the promisee, limit the promisor's estoppel, and protect the reasonable trust of the reasonable trust counterpart. It mainly emphasizes the reasonable trust of the promisee. Because of its pursuit of fair value, it has been fully developed in Anglo-American contract law in the 20th century. At the same time, this theory is also rooted in intellectual property law and has become the principle of estoppel in patent law. "Promise estoppel", also known as "promise not to go back on our word", means that according to the principle of good faith, the promise of a gift or a free promise made by the promisor is binding and must be enforced. The principle of estoppel refers to the content restricted or abandoned by the patentee in the communication with the patent administration department, which can no longer be taken out to confront the infringer in the future patent infringement litigation.