An independent claim typically includes a preamble portion and a characterizing portion.  The preamble generally describes the purpose, type or nature of the claimed invention, and sometimes may cite another claim.  A preamble of an independent claim should be considered when protection scope of the claim is construed. 

During patent prosecution, the actual definitive effect of the preamble depends on what impact it may impose on the claimed subject matter per se.  For example, in the construction of a product claim having a use feature in the preamble, the actual definitive effect of the use feature shall depend on the impact it imposes on the structure and/or composition of the claimed product.  For another example, in the construction of an independent claim containing reference to another claim, all the features of the claim referred to shall be taken into account, and their actual definitive effects shall depend on what final impact they may impose on the claimed subject matter of the independent claim.

Regarding a definitive effect of a preamble, the courts in the patent infringement litigation used to take a standard similar to that for patent prosecution.  For instance, in Judgment (2014) Gao Min Zhong Zi No. 2044, the Beijing Higher People’s Court holds that the plug connector module feature in the preamble of claim1has a definitive effect on the claimed holding frame because the plug connector module cooperates with the holding frame and is closely related to operation of the holding frame and achievement of the invention, whereas the plug connector casing feature in the preamble has no definitive effect on the claimed holding frame because it does not appear in the claim except once in the subject title and has no impact on the technical solution.  However, as prescribed by Article 5 of Judicial Interpretation II of Several Legal Issues on the Trial of Patent Infringement Cases issued by the Supreme People’s Court which has taken effect as of April 1, 2016, “when the protection scope of a patent is determined by the People’s courts, all the technical features described in the preamble portion and the characterizing portion of an independent claim and in the citing portion and the defining portion of a dependent claim are limiting.”  According to this article, the plug connector casing feature mentioned above is likely to be considered as being limiting.  In other words, after Judicial Interpretation II became effective, it is probable that a technical feature in a preamble will be considered as being not limiting during patent prosecution whereas it is considered as being limiting in patent infringement litigation.

Therefore, in order to prevent a patent from being construed as a narrow protection scope in patent infringement litigation due to a definitive effect of a preamble, patent agents need to avoid incorporating into the preamble any unnecessary technical feature such as a use feature or an environmental feature.  Furthermore, if a use feature or an environmental feature is believed to be helpful to withstand the invalidation proceedings of a patent, such a feature can be placed in a new dependent claim when the application is drafted.  In addition, since the weight given to preambles may vary from jurisdiction to jurisdiction, a patent applicant may need to amend the preambles, which are generally neglected when the application enters different states.