The Taiwan Intellectual Property Office published new Patent Infringement Assessment Guidelines in February 2016 to replace those released in 2004. The Guidelines serve as a reference for courts in judging patent infringement cases. In addition to the “tripartite test,” the sole test for doctrine of equivalents prescribed in the 2004 edition, the 2016 Guidelines introduce two new tests: "insubstantial difference test" and "interchangeability test."
According to the "tripartite test," a feature in an accused product or process is equivalent to a corresponding feature in a claim if the accused feature performs substantially the same function in substantially the same way to accomplish substantially the same result as the claimed feature. Pursuant to the "insubstantial difference test," a feature in an accused product or process is equivalent to a corresponding feature in a claim if the difference between the accused feature and the claimed feature is insubstantial. Under the "interchangeability test," the doctrine of equivalents applies if a feature in an accused product or process and a corresponding feature in a claim are interchangeable and a person with ordinary skill in the art would have known that the features were interchangeable at the time of infringement and they perform substantially the same function. Rather than prescribing specific criteria as to which of the above tests to adopt in determining whether doctrine of equivalents applies to a particular case, the Guidelines stipulate that the choice of test should be decided on a case-by-case basis according to the technology and facts involved in said case.