In the United States, the Jepson claim is popular.
A Jepson claim recites the prior art in the preamble, uses the transitional phrase "the improvement comprising" and then recites the new elements or improvements to the prior device or method.
Rule 6.3 of the Patent Cooperation Treaty Rules requires that wherever possible, claims should be written in this form. It is not necessary to write them in this form in a P.C.T. application if you have filed your application in a country in which the form is not mandatory.
Markush claim :
Markush claims are often used in chemical composition patents where a selection can be made from a "class" of claim elements.