which precedes the expression "characterized in that" or "characterized by" in a claim written according to the so-called "two-part form", and therefore everything which is regarded as known in combination within one prior art document, namely the closest prior art document. For this reason, in Europe, the preamble of a claim is sometimes also called "pre-characterizing portion". United States A claim may include the following parts: A preamble that recites the class of the invention, and optionally its primary properties, purpose, or field: "An apparatus..." "A therapeutic method for treating cancer..." "A composition having an affinity for protein X..." This preamble may also reference another claim and refine it, e.g., "The method of claim 1..." (See "dependent claim" below.). A "transitional" phrase that characterizes the elements that follow. The phrases "comprising", "containing" and "including" are most often used and (under some patent laws, specifically US) preferable, as it means "having at least the following elements..." and are therefore open (inclusive) and do not exclude additional limitations. The phrases "consisting of" and "consisting essentially of" are (under some patent laws, specifically US) more limiting, as they mean "having all and only" or "virtually only" and are therefore closed (exclusive). In the US, the phrase "consisting of" excludes additional limitations, while the phrase "consisting essentially of" excludes additional limitations that would "materially affect the basic and novel characteristic(s) of the claimed invention". A set of "limitations" that together describe the invention: "an X, a Y, and a Z connected to the X and the Y." The elements should be described as though they interact or cooperate to achieve the desired result. Optionally, a purpose clause that further describes the overall operation of the invention, or the goal that the invention achieves ("wherein the Z simultaneously controls the X and Y," or "wherein the Z accomplishes purpose W by controlling X and Y," etc.). "Wherein" clauses limit the scope of the claim. Other forms of purpose language are "whereby" and "thereby" clauses, similar to the "wherein" clauses just described, and statements of intended use in a claim preamble (depending on facts of case, preamble may or may not limit claim scope; in this case it was the "essence of the invention"). Interpretation or claim construction The claims often use precise language. Certain words commonly used in claims have specific legal meanings determined by one or more court decisions. These meanings may be different